Happened to me yesterday while playing NFS Shift 2.
I just presumed it was an overheat, so my PC switched of to prevent damage.
Could also be a quick HDD failure.
Worst case scenario your PSU is on its way out.
Driver issue, check sims is fully up to date, and Direct X and all the rest of it.
Any chance you could of accidentally lent on the reset switch?
I wouldn't worry to much over just one time
Intel Core i5 2500K /-\ 32Gb 1600mhz RAM /-\ Asus P8Z68/GEN 3
2x 256Gb Crucial M4 /-\ Crossfire XFX HD Radeon 7950 Black DD
Sound blaster Z /-\ yourpcperfect.com /-\ Windows 7 Pro