So if I read it right, your screen stays blank, but the PC is powered on, like lights and fans spinning?
If that's the case, try plugging the video cable into the on board graphics, maybe there's a problem with the graphics card, if you have on.
Also, if you have any other graphics cards laying around, try swapping one in.
On another depressing note, the one and only time I killed a CPU, this is exactly how it acted. So it could be a problem with that
Try unplugging all unnecessary hardware from the motherboard, like case fans, USB headers, expansion cards and hard drive. Maybe one of them are shorting it out.