internet cable said:
tried that and no dice, still playing up
As you surmised earlier the next course is to try a different PSU. See if you can borrow one from another machine or a friend to test this hypothesis before simply buying one. If your machine still does not boot then there are many potential causes to investigate. Next try your PSU in another machine and see if it boots with your old PSU. If it does boot then it is likely your motherboard. If it does not boot then it could be the motherboard still as well as the PSU or a nagging short in the PWR switch or RST switch of your case. I found a client's machine with just that.