|You still say nothing. So all I can do is to sock it to you in general terms.|
There is a possiblity your computer is getting infected with some sort of Malware. So I say --- Most Virus and Spyware scans are likely to work better in Windows Safe-Mode.
For example, back when the MSblast worm was infecting computers, Microsoft came up with fixes to plug up the hole in Windows XP. Such fixes resemble these below ▼▼
MS03-026: Buffer Overrun in RPC May Allow Code Execution
MS03-039: A Buffer Overrun in RPCSS Could Allow an Attacker to Run Malicious Programs
Also such fixes, old or new, are included in Windows XP Service Packs, or any other Updates.