I would test the video card. I mean, I can't physically see what is going on but what happens a lot of the time with vga issues that the comp does boot but you have no way of telling.
If you can reset the cmos (not sure if you can on Dells) I would try that. Also, when you are testing do as minimal a setup as possible, i.e. mobo, proc, 1 stick of ram, psu, vga that is it.