download and run this ... it has a "torture test" let it run overnight

its a well known pc testing tool

http://www.mersenne.org/freesoft/

if it has any problems then either your ram, cpu , mb etc are bad or overheating....

if it runs fine then you know it's a graphics card problem....

either way my bet is hardware issue, computer should never reboot like that ever.


Tips if this helps you any   1NvPSnFGXeok7ebj6JgttmozNbBVsuG63R