Sorry to be making two threads so close to each other, but I couldn't modify my previous thread title to explain this problem too.

I turned on my computer at about 2pm today, when it was last on about 6 hours before then it had been working fine. After it had been on for a couple minutes the keyboard and mouse (both connected through PS2) stopped responding, the keyboard wouldn't even light up the caps LED when I tried it, but the laser on the mouse was still on, but again not responding to clicking or moving. I hit restart, but the screen would just go blank and not restart, the computer would still be "on", but not responding to the power button or outputting to my monitor or anything. After turning off the PSU and then trying again it started up eventually, but again after a minute or so the mouse and keyboard stopped responding. I switched the mouse over to USB and it worked, and after starting the on screen keyboard the physical one started responding again.

I decided to do a restart with the mouse still in USB and the keyboard in PS2, again the mouse responds, and this time the keyboard has continued working too. The problem came when I turned the computer off, I powered down and then tried to turn it back on and had the problem I had before, the computer powered up, but wouldn't output any signal, even the light that shows the computer is connected to my router was off and it took multiple attempts at turning the PSU off and on again to get the computer to properly start.

Any help would be very much appreciated!