So I put an XFX 5770 in a Dell XPS 420 with a 375w power supply and no matter what I do I can't get it to display on any monitor. I've gone after every display driver manually and with Driver Sweeper; as far as I can tell nothing should conflict. When I turn it on with the 5770, the fans and lights turn on, but the computer doesn't seem to actually boot or do anything. Put in the old card and it works fine. Have reseated the card more times than I care for and have already reset CMOS battery.
I'm aware that the power supply is beneath what the stated requirements for the card are, but surely it would at least display something?
To me it looks like either the video card is bad or the power supply is so insufficient the stupid thing won't display at all. Is there anything I'm missing here, and if it is one of those two issues, any ideas how to figure out which it is?
Easy to find which is at fault. Try the video card in another PC. If it works there, something with your PC is the issue. A too low power supply to the video card can easily cause it not to display anything, it can even damage the card.
A 375 Dell power supply from an XPS system should be enough to power the card though, I think the card itself will draw a bit over 100watts at load, and I doubt the rest of your system will pull the extra 200+. Try to unplug any extra drives, DVD drives, and try it then. Just keep the main hard drive powered.
You may also have an issue with your power rail that the card is connected to. "with one 75W 6-pin PCI Express® power connectors "