I have a DIY computer, 2.2 GHz Athlon64 CPU, 2 GB RAM running XP Pro.  Occasionally, it is unresponsive.  Cursor moves, but it doesn't respond to mouse clicks.  No activity on hard drive, CPU utilization is low,  97% System idle process. I use Avira antivirus, don't think I have any malware running. The computer was built about 3 months ago. XP is updated Doesn't seem to be a pattern of what programs are running.
What can be going on?

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