have desktop pc wont turn on have put new psu in still dead have checked power cord ok, all internal connections checked and double checked please suggest other possible problems think may be motherboard is it possible to test before replace.
Try to disconnect front USB, front audio, harddrives, cd/dvd drives. Then you can see what might causes the problem.
disconnect all non essential components, try booting with only CPU, RAM, Grafx & PSU, then try to boot, then add 1 component at a time (making sure you can boot each time) when it does not boot that part could be faulty
Did you also connect the 4-pin power connector? (is located somewhere near the CPU area). I mean this thing:
Did you also connect the cables of the front panel in the correct way on the motherboard? (power / reset switch)
You would need thermal paste to guide the heat from the CPU away into the heatsink. Without it, the system will stop. You can find an article about it HERE
but i have not done anything to the cpu all i have done is installed a new psu because i thought that was the reason the system would not start
You'll need to do it if you have installed a CPU. Everyone needs to do that. This paste comes together with your CPU cooler. Install the CPU, put the paste on it (as a thin layer), and then put the cooler on it.