|When you say you can boot to safe mode do you mean you know which keys to use (since nothing is on the screen) and can hear windows loading? Can you tell if it boots to windows in normal mode?|
And you're using the same monitor with both cards and verify it's connected tightly to the card?
OK, it's not a power supply problem, it's not a resolution problem (since there's no video when you boot to safe mode), the slot is OK since another card works in it, the card works with another motherboard so it should be OK. . . I don't know. Barring a connection problem with the monitor I can't think of any reason it should act that way. You may have to beat it to death with a hammer and then buy new one.