Very odd problem

OK, the problem is if I plug my video card in the PCI-E slot but without connecting the PCI-E power chord the PC starts but it just beep's like no video card is inserted, if I connect the power chord the PC starts for 0.5 sec then shut's down, and I neet so disconect the power cable from the PSU to be able to try to start it again , the thing is that the LED from the card reader stays on even after the PC has shutdown, so what could be the problem? I tried without the video card (on integrated graphics and the PC works), even if I remove the video card from the MB and only connect the PCI-E power then try to start the PC with the video card on the table it shut's down. So is my video card busted or my PSU?

Video card is a HD4850

And the PSU a thermaltake 430W PSU

Thanks

CRISTI