Why your Computer Shutdown only 20 minutes after you Start it?

• Your power supply is probably going bad. It gets hot and then shuts down. It might also be a bad power supply fan, that is the power supply might not be getting hot because of a problem with the power supply but because the fan isn't coolingit properly.
  
  
• Another common cause for shutdowns is the CPU overheating. Check the fan to make sure it isn't spinning slow or seized, and that there is no dust in the heatsink. You can also check that the heatsink compound (the paste between the fan and heatsink) hasn't broken down.