LAN connection dropped, Internet OK

I have two WinXP-pro SR-3 machines on a LAN where they're normally linked to one another and the Internet via a D-Link DI-524 router. It works fine nearly always, but on occasion the LAN connection fails and the two machines cannot see one another, BUT they both can still access the Internet. By "see one another" I mean that Machine A can no longer print to the printer connected to Machine B, and Machine B cannot read the contents of shared directories on Machine A. NEARLY EVERY TIME when this happens, the background color of the start bar changes from Microsoft blue to a grey. Connection repair applications don't help. [Start|Settings|Network-Connections] .

Any ideas what causes this problem, and on how torecover without restarting the machine.
 
How are you accessing the network share? By IP address or hostname? Better assign static IPs to your machines.
 
My standard operating procedure has been to have router assign fixed IP addresses to the two machines in question, but in response to the comment, when I checked this morning I found one did not have a fix IP address. The problem I described has been happening off and on for at least two years. Originally, I let the router assign IP addresses, but I found that could lead to problems when multiple laptop computers were connected / disconnected from the network. Assigning fixed IP addresses cured that problem, but has not cured the seemingly random recurring loss of network connectivity. The Ethernet typically has two WinXP machines and a Synology Disk Station connected to it. The router is connected to the Internet via an ActionTech modem.

As indicated previously, a definitive indication of the loss of LAN connectivity is a change in the background color of the WinXP START window from what I'd call Microsoft blue to a grey. Restarting Windows on the main machine restores LAN connectivity. Power cycling the router that connecting the machines on the LAN does not help.

The loss of connectivity can occur an hour or two after all the machines are brought on line or many hours latter. The only action usually (but not always) associated with the problem is that it invariably occurs when my wife is in a hurry to print her NY Times Crossword puzzle that she has downloaded to her machine. She prints all documents by accessing the "shared" HP LaserJet 1000 printer connected to a USB port on the main machine. However, keep in mind that, she prints her crossword in the same way most every morning without problems. I could cure the NY Times portion of the problem by having a hard copy of the NY Times delivered every morning, but it would be a big waste to trash all that newsprint just to have access to a crossword puzzle.

Hopefully this provides the additional information requested.
 
1. Open up command prompt when the LAN connectivity drops and type in ipconfig /all. Reboot the machine - to 'fix' it, as you said - and perform the same command again when LAN is working. Post results.

2. How are you accessing the other machine? Via network places? Via typing in Explorer address bar - if so, IP or hostname?

3. Open up Network Connections, right-click on the LAN adaptor, Properties, and list what is in the little window under 'this connection uses the following items'.
 
You didn't lose LAN connection if you can still access the internet. Change in background color doesn't necessarily mean loss of LAN connectivity, maybe someone is remote accessing the machine (remote desktop).
 
Remove the NIC drivers or uncheck the TCP/IP Internet protocols then reboot the PC. Let Windows rebuild NIC connection again for your. Windows XP always had this issue that you describe. Also good idea to reboot all PCs on the network and power recycle the router. Make sure that one of the PC is your Master Browser for your Network on XP side there only needs to be one Master Browser so all the PCs can connect to.
 
My thought is conflicting IP addresses, which disrupts the whole lan.

a) don't use manual IP settings, instead use the routers Address Reservations via the MAC address

b) disconnect all system from the router and then add then one at a time and test Internet access before going to the next
 
1. Open up command prompt when the LAN connectivity drops and type in ipconfig /all. Reboot the machine - to 'fix' it, as you said - and perform the same command again when LAN is working. Post results.

2. How are you accessing the other machine? Via network places? Via typing in Explorer address bar - if so, IP or hostname?

3. Open up Network Connections, right-click on the LAN adaptor, Properties, and list what is in the little window under 'this connection uses the following items'.

THANKS TO ALL FOR THE VARIOUS SUGGESTIONS

(a) Re "St1ckM4n, post: 1270631" #1 - Inasmuch as I've not been able to recreate the problem, I can't acquire a detailed description of the status of the machine until I again encounter the problem. If I'm fortunate, that will not happen for several weeks.As indicated previously, problem can always be cured by rebooting the main machine, a DELL Dimension E510, but that creates short-term conflict when I'm in the middle of work session, and the wife needs her NY Times crossword puzzle.

Notes from the last time I was motivated to solve this problem where SONY computer can't print to HP printer connected to the DELL machine via USB port, are as follows:
11/Jan/2012 23:29 start panel color change indicates loss of connectivity to printer from networked computers. The local connection is still good (can print locally), and one can still print, BUT, if one tries to "Repair Local Area Connect" there is problem. IP address cannot be renewed. running these from command prompt don't help: ipconfig/all, ipconfig /flushdns when running ipconfig/all it says "IP routing enabled" = NO I don't know if that is normal state of affairs. However, after forcing "Local Area Status" to Close using Windows Task Manager, the START MENU again turned to blue, but SONY can't see DELL although it has Internet access.

(b) Re "St1ckM4n, post: 1270631" #2 and #3 If I go to: | settings | Network Connections | Local Area Connection |
the General Tab indicates I'm connecting via "Client for Microsoft Networks" and the RPC Service provider is "Windows Locator."

(c) Currently the D-Link router DHCP seems to assign IP 192.xxx.x.101 to the main DELL E510 machine, possilby because it is the first machine turned on in the morning, and specify a fix IP address of 192.xxx.x.105 to the SONY machine. Other fixed IP addresses are assigned to the NAS and the Tivo. My recollection is that at one time the main machine had a fixed IP address, but currently the router doesn't seem allow same.

I'm taking notes of all the suggestions, so the next time I encounter a connection failure, I can better document the problem.
 
THANKS TO ALL FOR THE VARIOUS SUGGESTIONS

(a) Re "St1ckM4n, post: 1270631" #1 - Inasmuch as I've not been able to recreate the problem, I can't acquire a detailed description of the status of the machine until I again encounter the problem. If I'm fortunate, that will not happen for several weeks.As indicated previously, problem can always be cured by rebooting the main machine, a DELL Dimension E510, but that creates short-term conflict when I'm in the middle of work session, and the wife needs her NY Times crossword puzzle.

Notes from the last time I was motivated to solve this problem where SONY computer can't print to HP printer connected to the DELL machine via USB port, are as follows:
11/Jan/2012 23:29 start panel color change indicates loss of connectivity to printer from networked computers. The local connection is still good (can print locally), and one can still print, BUT, if one tries to "Repair Local Area Connect" there is problem. IP address cannot be renewed. running these from command prompt don't help: ipconfig/all, ipconfig /flushdns when running ipconfig/all it says "IP routing enabled" = NO I don't know if that is normal state of affairs. However, after forcing "Local Area Status" to Close using Windows Task Manager, the START MENU again turned to blue, but SONY can't see DELL although it has Internet access.

(b) Re "St1ckM4n, post: 1270631" #2 and #3 If I go to: | settings | Network Connections | Local Area Connection |
the General Tab indicates I'm connecting via "Client for Microsoft Networks" and the RPC Service provider is "Windows Locator."

(c) Currently the D-Link router DHCP seems to assign IP 192.xxx.x.101 to the main DELL E510 machine, possilby because it is the first machine turned on in the morning, and specify a fix IP address of 192.xxx.x.105 to the SONY machine. Other fixed IP addresses are assigned to the NAS and the Tivo. My recollection is that at one time the main machine had a fixed IP address, but currently the router doesn't seem allow same.

I'm taking notes of all the suggestions, so the next time I encounter a connection failure, I can better document the problem.
How many network cards does your machine have? Routing will be enable to machines connected to more than one network (different subnets), your machine will act as a router (route data between networks). Complete "ipconfig /all" results would be very helpful. And the x in "192.xxx.x.101" are also important.
 
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