I have a dillema that got me pulling my hairs out... my pc wont detect my gpu, and im lost and out of options how to go about this. This is my current setup:

Machine is a Dell Optiplex 390 MT Win7 x64.

Mobo: Dell OEM.

Ram: 2x 4GB (8gb total) Crucial Ballistix DD3 1600.

CPU: Intel i5 2400.

HDD: Sata 500gb 128mb 7200rpm

PSU: EVGA 500w

GPU: EVGA Geforce Gtx 750 ti 2gb.

The unit wont detect my gpu, my bios is already updated to the latest version,(a11) and im unable to install any drivers because windows-nvidia installation keeps saying "there is no hardware detected in my system that is associated with this software". I have already tried uograding to windows 10 x64 (doesnt work either) going into safe mode and uninstalling the video drivers thru device manager and even using software like Display driver unistaller, and pluging and unpluging my gpu with the machine off and even on, and nothing..the fans are spinning on the gpu, but no matter what, the system doesnt detect my card; also when i connect the vga cable to the monitor and the card theres no signal and theres no option on the bios for video configuration, or to disable the onboard graphics and use the added card instead, or to add any devices. I know the card is compatible but am i  missing anything? Am I doing something wrong? Im at this point lost and cant figure out what to do. Any help is appreciated.