I know this is a semi-old post, but I had a situation where XP SP3 Pro sporadically deactivated and immediately locked me out of the system totally, no 3 day grace period. No access to system in safe mode. This is what I did to get back in. It worked for me, so I thought I'd post and it may be useful for others.
-Boot windows into normal mode.
-Click on your user if you don't have autologin turned on.
-It will tell you windows is expired, and give you the option to activate now.
-Click activate now, it will log you into windows, in a reduced function state.
-Minimize the "lets activate windows" window.
-Press "Windows Key" and "u" simultaneously. This brings up narrator.
-If it brings up the narrator help window, close it.
-On the main narrator window (it says "narrator can read aloud menu commands..." and has check boxes) click on the icon in the top left of the window that is a screen with a speech bubble.
-Click "about narrator." This brings up the info about narrator.
-Click the link on the info window that says "microsoft web site." This opens IE.
-Once IE is open, go to the address bar and type in a directory on your system (i.e. C:\Program Files\, or whatever)
-When you do this, it will cause the taskbar to appear for a brief period of time.
-Click Start>Run
-Type cmd and hit enter in the box. This brings up the command line.
-In the command line type the following lines hitting enter after each:
regsvr32 regwizc.dll
regsvr32 licdll.dll
rundll32.exe syssetup,SetupOobeBnk
-Note: Explorer only runs for a short period of time before it disappears, so you may have to try several times. To get the taskbar back so you can try again, simply enter a directory location in the IE main bar again. You don't have to get all the commands in one session, in fact it probably would be difficult to do so.
-Restart the computer, it should log in normally now.
After doing this, it allowed me to log into the system again and it reset activation so I have 30 days to get it activated now.
The information above, I can't take credit for, so I will credit my sources below. Credit for the first part goes to
this blog and credit for the command line commands go to TimeParadoX and kimsland in this thread.