Desktop turns on, but OS does not boot

Hi all,

I was using my desktop when all of a sudden I got a system service exception BSOD. It was taking a long time to collect data for the minidump file, so I held down the power button to turn off my computer. When I turned it back on, nothing showed up on my monitor besides HDMI/Analog on the screen. So I didn't even get a chance to try using my computer in safe mode.

My computer: HP Pavilion p6120f Desktop PC Product Specifications | HP® Support

I only upgraded the power supply to an OCZ 550w and I installed a radeon HD 6790 PCI Express 2.1 x16 a few months ago.

Any help is greatly appreciated!

Not 100% if this is related.. a friend of mine turned on his laptop and whilst it was loading up he got the cable for the power supply tangled up. He pulled it out and the screen went blank.Every time he turns it on now he gets a blank screen, cant figure out why?