i've just bought a DFI Lanparty UT NF4 Ultra D, X1800 XT, 3700XP CPU all running on a 450 watt PSU with 24 pin connector. Everything went fine put mobo/cpu into the case added all bits no probs. PSU details here http://www.jeantech.com/450.htm
However when i come to press the on switch the machine doesnt start. Both the motherboard lights come on and for a split second the PSU fan comes on as does the system fan and Video card fan but then everything dies although motherboard lights stay on.
I really can't figure out what's going and why its not working any ideas much appreciated.
Edited to Add: I didn't run the system out of the case to start with is it worth doing this?