Dell G5 desktop compatibility with older Radeon cards

[winston9t4]

Had an odd thing happen with a new Dell G5 desktop. It originally came with a Radeon 5700XT, everything worked fine. I wanted to put in a lower end card, and tried 2 Radeon 6450s and a 5450, and all 3 produced no video output, just a black screen. Went to a Radeon R270, and it works.

Any ideas what is happening? I was hoping to get the system working with a lower end card, but it seems to be incompatible in some way. Never experienced anything like this before. Thanks for any help!

 

[cdabc123]

Uefi vs bios conflict?

 

[pendragon1]

thats what i would suspect^^^. the 6/5000 card are legacy only, i think... look in the bios for csm(leg and uefi), something like that.