Look in Reliability History/Monitor and Event Viewer for error codes, warnings, and even informational events being captured just before or at the times of the crashes.
PSU: make, model, wattage (650 watts ?), age, condition (original to build, new, refurbished, used)? History of heavy use for gaming, video editing, etc.?
Disk drive(s): make, model, capacity, how full?
What specific games by title? Source?