This problem happens when a system is infected. install, update and run
antispyware programs like Adaware, Spybot Search & Destroy. CWShredder, The
Cleaner, and scan the system with an up to date antivirus. If after doing
so, you still don't have full control of your system, take ownership of the
C:\drive in drive\Properties\Security. Done in normal mode in XP Pro after
disabling simple file sharing, and Safe Mode in XP Home, check the KB
article for instructions.
How to take ownership of a file or folder in Windows XP
http://support.microsoft.com/kb/308421/en-us
KB article 308421 describes how to take ownership of files or folders that
you may not have permissions for if you are an administrator for that
computer. This article describes how to take ownership of a file or a folder
where you have been denied access.
Download Adaware SE Personal, Spybot Search & Destroy, CWShredder, and The
Cleaner.
http://www.majorgeeks.com/downloads31.html
Download The Cleaner
http://www.moosoft.com