Bandwidth maxing out

[Michelle2]

For some weeks my offices incoming internet access has maxed out. This has only been going on during Monday to Wednesday making it impossible to use the internet or to access the LAN over the VPN.
I have put an IP range block for 3 subnets on the Cisco ASA firewall, however alot of the Internet pages will not load properly missing images tables etc for example microsoft.com or they do not load at all.
If I release the IP range block we lose our access again. I know something internally is trying to access a website - or trying to send information back to this IP range, however I cannot find which system it is. I have checked network use on local systems, shut each pc down within 5 minutes to see if the line frees up, checked everything bar the coffee machine for viruses using 3 different av packages.
Does anyone know of any software which I can install which will monitor the PC's Network/Internet access?
Please dont suggest Ethereal or such like as my colleague tried this against my wishes and now has 7 years of information to read through!

Thanks

 

[DelJo63]

try logging all new connections in the Cisco router.

 

[Nodsu]

Are you sure it is something from within your network and not someone from outside flooding your connection?

The easiest thing to do would be to ask your ISP if they can provide you with some connection statistics.

 

[DelJo63]

hum; doubtful the ISP would appreciate or fulfill the request -- it's an issue the
user should be able to solve (from the ISP perspective).

this product looks promising

here's another

 

[Michelle2]

Thank you all for your replies.
I took the logs from the cisco ASA which is how I found the IP's causing problems, all be it one number different each day. I contacted my line provider who advised they know of a company who have in the past latched onto peoples lines and that I will need to put a ban on their IP range which is over 3 subnets! On doing this the line is now freed up. I can log in to my user account on the ISP service software to see the line stats.
However I am sure that it is an internal problem that something is trying to send information somewhere, and I am still unable to see which PC is causing the problem, but will have a play with the two software apps recommended.
Thanks again for your help