Basically, whenever I play games or watch videos, I always run the chance of encountering this issue. What happens is that my mouse freezes on screen & the sound suddenly starts sounding garbled, as if it were lowered several octaves. At that point, mouse function is dead. I can still use keyboard functions. However, I can't seem to turn off my computer via the desktop or task manager. I end up manually shutting down or restarting the computer.
I don't know if this would be a hardware or software (drivers) issue.
I only recently built this PC (first one actually) and here are the specs.
Windows 7 Home 64
80 GB PATA Drive (Cannibalized from my dad's old PC, plan on replacing with a 250 GB SSD in the future)
CD Drive (Cannibalized from my dad's old PC)
ATX 520W PSU (Also cannibalized)
Cooler Master Elite Case
Check that your power supply is delivering the required ratings. Get a new hard drive, the Pata drives are really slow and can cause these problems. Although I think the main problem is with your PSU. It seems to be worn out.