Question about a computer i am building?????help!?

i am building, or have just built a new server.....everything is connected properly...and i have checked everything 3 times.....power supply the whole thing.....however, when i power the computer on it stays on for about 30 seconds and then it just clicks off.....the num lock on my keybord freezes and stays on and i have to unplug the computer and re plug it in in order to get it up again.....when it comes up it starts running the mem test showing how much memory has ped....it shows the detection of the CPU as well....etc etc.... when i push f2 to go into my bios set up screen etc.... i can motor around in there no worries until it cuts off? why the hell is this happening? is it a jumpers issue? i checked all the jumpers that came pre installed in default on the board....tyan board s5211-1u ----