windows xp

You probably have a virus. Try downloading latest AVG free edition from grisoft.com.
You may need to do this on another computer and save it to cd or flash drive to install on the failing computer.

Any current antivirus should detect and remove this virus. You may have many. There are also Windows patches to make your computer invulnerable to this particular exploit. Run windows update from the start menu to update windows. You probably won't be able to do this until you remove the virus.

when the computer restarts
go to run and type shutdown -a
then turn off system restore.
download stinger.exe and update your virus scanner and run it.
download the patches from Microsoft
then restart the machine rerun the av program if it comes clean then turn on system restore

Sounds like the blaster worm.

Here is a link to Symantecs removal tool for blaster.

http://securityresponse.symantec.com/avcenter/venc/data/w32.blaster.worm.removal.tool.html

There are a few other viruses that exibit this same behavior.

Go to http://securityresponse.symantec.com/ to do a little more research.