New Graphics Card trouble

[Saterous]

I am stumped and was looking for some help.
I recently bought a GTX750ti to upgrade from my current graphics card.
Installed it, but the PC wouldn't boot. It would freeze my PC during the initial boot.
Tried the new card in another PC, and works fine. Installed the old graphics card and it would boot fine.

Figured out that my power supply wasn't sufficient to run the 750ti and replaced it with a Cougar 500w power supply. It's got 38.5amps on the 12v rail which is more than the required 20amps that is recommended on the card.

Well, same thing even with the new Power Supply. It freezes during initial boot, but the old card works fine.

My current PC Specs are:
Hewlett-Packard HPE-750t
Intel i7 2600 CPU @ 3.4GHz
Cougar 500w Power Supply
Geforce GT420 Graphics Card
Motherboard: Pegatron HP: Cleveland-GL8

So do I need another motherboard to get my GTX750ti up and running on this machine? If so, what would work with my setup?
Or is there another solution to my problem?

Any and all help is greatly appreciated my friends. Thank you.

 

[Whocandream]

When buying a new GPU you must Uninstall the old drivers. It's also very likely that your motherboard dosent support that card if you're running a GT card. It's also possible you're bottle nicking which is having on part better than all your other parts. So you might need to upgrade your cpu or ram.