Remove everything but the video card and try it, see if you have video. This means with CPU, RAM and keyboard installed, of course.
Try moving the video card to a different slot, if it's a PCI card.
Check for socket creep by pressing anu socketed chips into their sockets, be careful not to bend the motherboard.
Check to be sure the CPU is fully seated, often it can be only partially inserted.
If all of this fails, you're left with bad cache, CMOS chip, motherboard or weak power supply. Could also be the power supply does not produce enough wattage.
Soon as I come up with all the answers...they change the questions!!
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