My PC (running on Windows XP Pro) keeps shutting down whenever I try to do a virus scan or defrag. Please advise

Hi Treat your self to fixit 4 and run a Registry Defrag, thats how i have managed to get up and running many times. I dont know how it can be done with windows alone! maybe some one else can put you right. Best of luck!

You may have a virus or trojan or worm or adware or some other sort of malware. Run an AV scan (although I guess you can't), and download AdAware and Spybot, install them, update them, and run. Delete anything that looks suspicious. Some advise deleting everything because it's all reversible. Also get Spyblaster which keeps a list of bad stuff on your computer and blocks them from being installed (theoretically). Be sure your independent (not MS’s) firewall is enabled. If you had in mind running Hijack This as well, and posting your log, don’t until after you’ve run the two programs below. Then if you want to run HJT and post the log, do so in the Security and Virus settings and say you’ve run these two al-ready. If you don’t do this, the forum moderator will delete your post. Don't know what AV program you use, but if it's a program you already have like Norton or McAfee, try house call at trendmicro.com and see if that runs without shutting the computer down. Spybot AdAware

Shut off all running background programs. Turn off your screensaver. Check you power options "ensure it is on always on". Or try the virus scan and defrag from safemode. I forgot to add run a disk cleanup,clear your cache and cookies and empty your recycle bin too while you are @ it.