My guess: it's either the Video Card or the RAM Cards. If you have a video card issue, try plugging in an external display. If it's RAM, then the PC will not boot at all. One thing you could try doing to test the RAM is to unplug the RAM, and see if the PC does the same thing. If not, then the RAM cards are fine.
I don't have the PC model, so I won't be of too much help. But, I have worked with hundreds of PCs and Macs in the past.