I took out the CPU to replace the cooling paste and replaced the RAM. Now computer won't boot.

[civic ibex]

I took out the CPU to replace the cooling paste and replaced the RAM. That's all I did. Motherboard doesn't appear to be dead because the RGB lighting is still on and when I hit Start it temporarily kickstarts the fans.

But it won't boot. Even tried putting the old RAM back in. Can anyone guess what's wrong?

[civic barn]

See if clearing CMOS helps. (Note: on newer motherboards, removing the battery only freezes the clock. You must find the pins and either jump or short them. Refer to your board's manual to see where and what to do.)