GPU works in old rig but not the new one??

sympler

Honorable
Sep 1, 2013
48
0
10,530
So my original system was an i7 4770k with 256 ssd and a 500w psu with a XFX R9 270x. works fine so i want an upgrade to a gtx 980ti so i thought why not build a computer for my friend so i got a small case and an i5 4960 and a 500 ssd and a 850w psu. I put the 850w psu in my personal computer so the other system has a 500w psu now. so the XFX r9 270x works fine in my rig but when i put it in the new rig its doesnt work and yes without the graphics in it works but when i put in the gpu in i get no signal is given out. but has no problem in my personal rig tho....
Any ideas to why that is a problem?