Black screen when installing new GPU (from AMD to Nvidia)

[WhiteDeath]

So, i recently bought Palit GeForce GT 720 Silent 1Gb DDR3 graphics card, to replace my old AMD Radeon HD 4350. I uninstalled all AMD drivers from my PC and then i installed my new gpu into the pcie slot. But when i turned on the PC, all i had is black screen. When i put my old gpu back in, it works.. Any help? Maybe and hardware incompability? Is my PSU not strong enough?
My pc:
Intel Core 2 Duo E4700
4Gb ddr2 ram
Motherboard: Asus P5LD2-SE
PSU: Eurocase 400W 300XXV2

 

[Mohd Mamat]

Try RMAing it, could be a faulty GPU. Did you install the required nVidia drivers in safe mode before you mount the GPU in or use another display port to try it (vga/dvi)