Windows XP slow to respond after idle time

[geneprof]

After sitting idle (with or without a screen saver on) it takes 4 minutes and 30 seconds for my computer to respond. This started about three days ago and seems to occur when I've been away for 10 minutes or more. The cursor will move, and if I click on icons or open windows, the action will eventually be taken. The lag time has been increasing; at first, it was only about a minute. I haven't downloaded anything lately, and the temperature is fine. I checked the task manager afterwards, and nothing unusual seems to be running. Has anyone had this problem, and do you have any suggestions? I'm running Windows XP Pro 5.1 on a 1533 Mhz PC.

[GX1_Man]

What are you using for malware protection? You should also check your running processes with task manager, but I bet you have malware issues.

[geneprof]

I have Ad-Aware SE and just tried running the MS Windows Beta "clean-up"- both report no problems.

[geneprof]

I just checked the task manager again. CPU time is about 1%, PF Usage is steady at 378 MB, the system idle is around 98, and no unusual processes are listed.