GPU Not Displaying

[Pc-noob616]

So i bought a prebuilt dell, upgraded the ram to 16gb, psu to a evga 550 watt, and put my old hard drive in that was in my old pc. then i put in my gpu (its a radeon r9 270x) and i connect the dvi cable to it and it doesn't display anything which is weird because i was using the gpu in my old pc the night before with no issues. So i checked all the connectings and all of it is connected but the weirdest part is i have a old shitty gt 710 and when i plug that in it works fine but my r9 270x doesn't. And when i look in bios it says that there isnt even anything in the pci e slot in the mobo. but the gpu fans spin and the part that lights up when both 6pins are plugged is lit up too.


So can anyone help..

 

[Pc-noob616]

oh and btw the dell is a Dell Optiplex 990 micro tower with an i5 2500, 16gb of ram and the normal dell mobo if that helps