My CPU turn off unexpected! I don't know WHY?? Please help me!

[anskey10]

I'm administrating a small Internet room, suddenly the PC that is SERVER turned off. It's turn off unexpected three times in this morning. I think the problem is HDD because my SERVER action day by day! (Right or wrong?)
Please help me solve this problem!

PS: I'm beginer in ADMIN & English. So,it always occur mistake.
Help me !!!