Games Shutting down my PC

[Paolos]

I've just built my new PC but for some reason the power only stays on when it's placed on its side. And, when I tried to play BF2 it turns itself off when it's loading. Any ideas what this could be?

 

[Paolos]

Thanks for that! I can actually play BF2, but only on the lowest video settings. If I try to crank it up any higher it cuts out .... most frustrating.