hp turing off my its self

[sabledog]

i was working on a friends hp with win me p 111 ,633mhz, 128 ram, 37 gb hard drive..
when using a pc esp. on interenet.. the pc just shuts down and restarts, like i just powered off the pc with out correct shutdown...does scan disk afterwards...im thinking is a bad power supply... pc is just a little over a year old...
please help.. thanks

 

[brianF]

Check that it's not overheating, if a fan was out or the case vents blocked it may be shutting itself down for overheating.