Auto restart and other problems

Hi
I run Core 2 Duo E6750, Intel DG33, 2GB Kingston Ram, 160GB HDD, integrated VGA, Windows 7 Release Candidate

I've been having this problem for a while. When i switch on my PC A black blank screen with a something like this " _ " appears on the top left hand side of my screen. Then after about two or three miniutes the OS activates showing the Intel Screen and then windows starts.

And now the computer makes a big sound and automatically switches off in an instant, after about 10seconds it restarts like explained above

Pls help me here!!!!,,PLSSSZZZZZZZZzz

Apurva Wasala \m/