I have a computer at the moment which will not POST.
I have disconnected everything from the main board except the PSU and the CPU/HSF. I have tested the PSU with a reliable one and it boots another system fine. So we can cross that off the list to check. I have got the main board power connector plugged in and the 4-pin CPU power connector plugged in and that is it.
The leds and fans spin up however nothing displays on the monitor and no beeps are heard from the motherboard either.
So i am led to believe from reading several posts on the forums here that the motherboard could need replacing??
In order to POST successfully you also need to have your RAM installed. It will never post with no RAM in the machine. It could very well be that your RAM is the issue here. If you have several sticks in your system try booting with just one installed. Try this in every single slot on your motherboard and then swap and do the same with your other stick. This will eliminate the possibility of a bad RAM stick since both are unlikely to be bad.
You may also want to ensure that your heatsink and fan unit are mounted properly. It's not likely, but I have seen some systems not boot because of small things like this that are often overlooked.
It may also be worth you having a look over this guide:
It's a very good guide to basic boot issues etc. and may just help you identify any other issues it could be. You want to be sure its the motherboard before you shell out and buy a new one. Even if it takes you a while to go through all these at least your 100% its not something else! Hope this helps and good luck!