DELL 8300 16 MB 780 WATT power supply 8MB RX 480 black screen! Boots fine with original graphics card.
It doesn't look like that motherboard supports UEFI, only the A07 BIOS does which isn't for that revision of the motherboard. So that is most likely the issue.
Please provide more information, we'd like to help. For example, what is the make and model of the Motherboard and what was the original graphics card?
Have you updated your Motherboard bios to the latest revision?
INFORMATION REQUIRED WHEN POSTING A QUESTION
It's a DELL OEM MB! I upgraded to a 650 watt power supply. I'm thinking the PCI slot isn't compatible. PC doesn't finish booting. I put the original GPU back in and boots right up
Have you tried updating the bios to the latest available on the Dell website for this system?
Product Support | Dell US
PC is updated to all the latest drivers and BIOS
Retrieving data ...