[NAME]  [NAME]  390 790 990 does not have UEFI bios and therefore will not run R series card. Max card for these models is radeon HD 2000 3000 4000 5000 6000 7000 8000 series. Radeon HD7470    160164167166161 Low profile Radeon HD7470  B00CR230G0    
Hello, I've had this Optiplex 390 SFF for quite a while, even been through a mb replacement, now I usually run a gt1030 in this system but I've been trying to get another card - a Radeon R5 240 1gb working, unfortunately it doesn't show up in task manager, device manager or even as taking up a pci slot in bios, my question is is this card even compatible with my system? 
Dell Optiplex 390 SFF R5 240 Compatibility