If so I'd point the finger at a thermal trip on your CPU (check your heatsink is correctly attached, thermal paste applied, and fan running). Other than that probably a motherboard or PSU failing.
Without more information it's hard to say what the cause is. Perhaps your CPU or GPU is overheating (perhaps both). A program like HWMonitor can help you determine that.
Perhaps your power supply is being over burdened or getting old and you need to replace it with a good quality PSU that can provide the necessary amount of power.
Perhaps your Windows OS has become corrupted and you need to re-install it. Or maybe you just need to update the graphic card drivers.