PC powered up, no display

[lorenzooo_]

I recently purchased a graphic card and PSU and tried to install it into my PC. The graphic card GTX 550Ti and PSU of 650 watt (true watt around 390 - 420), failed to powered up my PC with GPU installed. However, the installation of GT630 is fine with the PC.

What I have tried :
- Cleared CMOS Battery
- 6 pin PCI-E is plugged in (firmly plugged in)

About GPU condition, they're fine, tried it on my friend PC working flawlessly ; in fact he used same PSU like mine but with molex connector (500w of PSU same brand model but mine is basically higher and better)

Installed GT630 my previous graphic card, worked on my computer but the GTX 550Ti not working on my PC.

By the way, my specs are (just in case if needed)

Processor : Intel Core 2 Duo E8400 3.0GHz
RAM : 2 GB X 2 800MHz DDR2 (4GB RAM)
Motherboard : Gigabyte G41M-Combo
Hard DIsk : Western DIgital 500GB
Optical Disk Drive : Asus x24 Green DVD Writer
PSU : AVF 650W (390w-420w) - should be able to run the card, i'm 100 percent sure
GPU : Currently using GT630 working fine, but having probs with GTX 550Ti
Using VGA cable of HP L1706 plugged to the graphic card.

RAMs are working fine.

 

[Vetsku]

Did you uninstall the drivers for the last card you had?

 

[lorenzooo_]

Did you uninstall the drivers for the last card you had?

Yes, I did.