Okay, so I'm having a strange issue lately with my desktop, and off the top of my head I'm not sure what the problem is, so I'm hoping for some ideas on how to track down the cause.

First, my PC:

AMD Phenom 9600 Quad-Core 2.4 GHz
4 GB DDR2
160 GB boot HDD
1 TB & 120 GB secondary HDD
Nvidia GeForce 8600 GTS
Windows 7 Professional 64-bit

I have my power settings as follows:

Turn off the display: 10 minutes
Turn off hard disk: 20 minutes
Sleep after: Never

After a while, I'll come back to use my computer again, wiggle the mouse, and the screen comes back on like normal, but the desktop is unresponsive. I can move the cursor, but nothing responds to clicks or keyboard entry. If I click a few times with the mouse, the computer eventually locks up completely and the mouse cursor stops moving as well. After I restart, everything works just fine.

Is there a log you recommend checking or really any suggestions would be welcome at this point.

Thanks!