The GPU I had installed on my PC is GT 210. I uninstall the nvidia drivers and rebooted it. Then, I turned off the computer, installed the 7870 onto the mobo and connected one 6 pin to it (my current PSU has only one 6 pin, 7870 has two 6 pin slots). When I start up I get no signal on monitor, cannot see BIOS as well. Next I remove the 7870 and start up with onboard so I can get into BIOS and disable onboard graphics and enable PCI. Then I reinstall the 7870 and connect the 6 pin and then start it up, still no signal. I reinstall Win 7, repeated steps above and still wont work.
I have tried using Driver Sweeper in safe mode to remove any traces of Nvidia drivers.

Notes: I am using a DVI to VGA Adapter since my monitor only has VGA. The fans on the 7870 do spin. When I disable onboard and enable PCI while using GT 210 I get signal.

Specs:
CPU: i3-3220 3.30 GHz
Mobo: GAB75M
PSU: CM 500 watts
1st GPU: GT 210

Any help is appreciated.

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XFX 7870 DD No Display 2dakgt5