Don't laugh:
Make sure you can get a lamp to turn on in the electrical sockets where you plug in your computer & monitor.
Make sure the switch on the back of your psu is "on."
Use your motherboard diagram and carefully, slowly, re-verify that each wire you installed, especially the wires from your computer case, are to the proper connections.
Still not firing up? One thing people sometimes have to do is remove their motherboard and set it on a piece of cardboard or wood table (nonconductiive) and see if the beep codes will sound off with power on. People find that on rare occasion a foreign object like a motherboard standoff screw fell behind the mobo causing an electrical short between its underside and the case wall. Unlikely, but still a possibility.
Well I took out the CMOS battery and switched the jumper for about 5 minutes
Good work, that's the right way! You did good there.
I usually leave it longer but people on this web board stereotypically argue against it, insisting the charge is instantly grounded out. People on other boards like DIY-Street and Xtreme Systems recommend the opposite, to leave it off a even up to overnight, because there can be a tiny remnant charge that takes a long time to dissipate. Rigs that seemed totally dead have been revivified by leaving the jumper on "clear"with the cmos battery out and the power cord ophysically unplugged from the psu overnight, for many hours. I don't mean to be argumentative, but I completely disagree with jackschmittusa's post above, based on real experience building many overclocking rigs.
Another thing is to see if your mobo manual tells you which keyboard key to hold down during power-up to forceloading of default valueds in bios. That saved my butt on one rig I built, it wouldn't run, then I did that and it posted.
