Some motherboards have a CMOS reset button and others just have jumper pins where you move the jumper from like pins 1-2 to 2-3. Where you leave the jumper in place for say 30 seconds. If the pins don't come with a jumper then just use a screwdriver tip to short across the appropriate pins for 30 seconds. Many times the CMOS jumper pin block is near the button battery but not always. Consult your manual.
Before you short the jumper, however, power the machine down and remove the power cable from the back of the PSU. Hit the power button to drain the capacitors then jumper. Before you power back up, move the jumper pin bridge back to the original position if there is a jumper bridge.
But first, check #1 below.
Other things to check:
1. Make sure your RAM is inserted into the correct slots on the motherboard. When you aren't filling all the slots, you have to put the sticks in the right slots. Check the motherboard manual.
2. Make sure CPU is seated correctly and that there are no bent pins underneath. Of course, you'd have to remove the water cooler heat block and that is a pain. But we've had inexperienced builders find that to actually be the problem. Make sure you laid the CPU in the socket in the right orientation. One of the corners has a gold triangle on it that matches the triangle pattern on the socket. You can also turn the CPU over and observe the pattern and make sure it matches the one on the socket base since there are places where there are no pins.
3. Remove the motherboard and make sure there are no standoffs unaccounted for. A standoff in the wrong place will short on the circuitry on the board's underside.
4. Replace the PSU with a known working one.
5. Take your new PSU and swap it with the old one in the old computer to make sure the new PSU is good.
6. Take the video card out of the old computer and swap it with the one in the new build.
7. Try your new video card in the old build.
Let's be clear here. You're not getting any post on the monitor?
