dai

cmos reset
turn the computer off
remove the power lead from the back
take the side off
remove the cmos battery
move the cmos jumper from pins 1 and 2 to pin 2 and 3 and the back to pins 1 and 2
reinsert the battery
put the side on
replug in the power lead
boot the computer

there can be 2 solder points you touch with a screwdriver
2 pins you touch with a screwdriver or use a jumper
a cmos clear switch or button
there will be a diagram and instructions in your manual

if that does not get you post
leave the computer shut down for an hour and see if it boots
if it does redo the paste on the cpu with some arctic silver

if not see if you can borrow another quality 550w or better power supply to try in it