XP Permission problem. Can't do anything!!

I have Windows XP SP 2 and I have been using the same Administrator account for the past 2 years without any problems. The problem started abruptly this morning. I booted my pc and used it for an hour without any problems, checked my email, updated AVG, uninstalled some applications, used DC++ etc. After some time i wanted to uninstall some more applications but i get this error when i double click Windows Add or Remove Programs:

"Windows cannot access the specified device, path, or file. You may not have the appropriate permission to access the item."

Now i cannot adjust my time, uninstall applications, launch AVG (get same error), run DC++ or do anything at all!! When i thought of posting here I thought i would post a Hijack This! log but can't even do that!! Also, when i boot in Safe Mode everything works fine. So I booted in Safe Mode deleted my current Administrator account and created a new admin account and restarted but I get the same message whenever I try to do anything. Get the same problem when I log in with the default Administrator account. I even did a repair install of XP but the problem still persists. I don't want to do a format and fresh install of XP because I have a lot of important stuff in it.

Please help!!

 

Have you tried "sfc /scannow" with your OS disk in the Drive, this will replace and or repair OS files?

Also you could goto "services.msc" and compare what is enabled and not enabled by following this guide, you may have deleted or modified a service you need:

http://www.blackviper.com/WinXP/servicecfg.htm

Be careful and dont "delete" things you may inadvertantly need. Also update to SP3.

 

you also might want to check for malware . Run thru the Malware removal process

 

Hey plodr thanks for the tip. Looks like AVG was the culprit. I always keep AVG on all the time. The day this problem started AVG was not launched. I booted to Safe Mode and uninstalled AVG, problem solved. Thanks everyone for your help.