Strange Boot up Problem

Hi guys,

My friend asked me 2 look at his computer, its got a strange problem. When booting the screen will go blank. I’ve tried safe mode, it loads all the drivers just fine then the screen just goes black and the restart button on the front of the comp doesnt work, nor does the power button so i haf 2 pull out the power cable.

I’ve replaced the power supply with a working 1. I tested the memory with memtest, and used the seagate diagnostic util to test the hard drive, both came up fine. Gfx card is okay. I’ve rest the CMOS.

When i did open it up it was caked in dust! A layer of it on the cpu heatsink. I managed 2 get most of it off. CPU temp seems normal.

Any suggestions? Hardware or software prob?