I just installed a new 4850. I start the computer and everything sounds the same except that there's no display. Doesn't matter whether I connect it to the video card or the integrated. When I take out the video card, the integrated video works again.
Athlon X2 545
4 GB DDR2
585W PS that came with the case
Tried disabling the integrated graphics in device manager. Also checked the BIOS and set it to detect PCI-E slot. Still doesn't work. It POSTs but no display.
Make sure its pushed RIGHT in, even if you have to force it, The amount of times I've done this and paniced when all along the card just wasnt seated properly, Have you connected the PCI-E power connector, also check the recommended power supply for the card.
Finnally look on your psu and look at its ratings and ampage etc. most PSU's that come with no brand cases are pretty crap, mine failed on me with a radeon 3850 and it was a 500 watt, but rubbish quality
I managed to get the integrated graphics to work while the video card was plugged in. Got to windows and checked the device manager. It said that the card was plugged and working. I updated the drivers but it's still the same.
It's not the worst PSU, but I doubt it will operate for long over 300W... the 585W figure is "max" and not really likely anyway. Probably capable of 450W max for a few minutes.
A 5850 is only going to pull 2 amps 12V at idle though.... do you have BOTH 6-pin power sockets on the end of the card filled? You need two 6-pin PCI-E cables for this card to work, and your max load will be somewhere in the neighborhood of 250W.
Get a decent PSU such as a Corsair VX550 or perhaps an Antec.