So if you select "last known good.." you can boot up into windows?
Lets first try cleaning abit:
(in safemode if needed)
Please download
ATF-Cleaner.
Run ATF-Cleaner:
First check "Select All" , and then remove the tick infront of "History".
Then click Empty Selected.
When you get the "Done Cleaning" message, click OK.
install and run RegSupremePro. It will want to make a backup of your registry , let it. Once it has finished, click on the Registry Cleaner tab, select Aggressive. When it has completed, click on Select, choose All. Click on Fix, and let it fix everything that it finds.
http://www.majorgeeks.com/download4256.html
Then go to start/run and type
sfc /scannow and press enter , have youre XP disc in youre drive.
If that doesn't then go to start/run/msconfig and disable everything on the startup tap and see if the problem is still there.
If that also doesn't then lets have a look for malware , please follow the instructions for that in the "Prework" link below in my sig.
Or try a repair install of windows:
http://www.microsoft.com/windowsxp/u...ps/doug92.mspx