I have a 4 year old self built pc which works fine. I decided to change the graphics card from PNY NVidia Quadro FX1300 (fan) at 55W, to an XFX ATI HD5450 (no fan) at 20W, before handing it on to my son.
Without changing any hardware, settings, drivers or BIOS the FX1300 works every time (both before and after trying the other graphics card). And every time the HD5450 gives only a black screen: there is no POST, no beeps, no writing, no image, no progress, but the fans work and the HDD led is on.
There is nothing wrong with the computer or monitor: as soon as I switch back to the FX1300 everything works just right again. So please don't reply with RAM, PSU, seating etc solutions because it is clearly a graphics card issue. But what? I'm stumped.
If the nvidia drivers are still installed it will not boot on an ATI card. From your original post "Without changing any hardware, settings, drivers or BIOS the FX1300 works every time (both before and after trying the other graphics card)"
sounds like a bad video card to me or it isn't seating properly.
HD5450 successfully tried in Asus M4A89GTD Pro/usb based computer. Note that the BIOS had to be set for the PCIe16 on the Asus whilst running the onboard graphics, before physically inserting the HD5450 board. When I reverted to onboard graphics I had to re-set the BIOS whilst the using HD5450.
I have now been told that the 'non-working HD5450' problem is non-compatibility between the vs2.1 PCIe16 of the HD5450 and the vs1.0 PCIe16 of the original MB. Yes, I thought PCIe16 2.1 was backwards compatible but it appears not, at least with the ATI 5xxx series. And the HD5450 works so cannot RMA it.