No monitor output

My brother has important (unbacked) up data on his pc but somethings packed up, the symptoms are...
The monitor shows no signal when the pc is running, so far I've...
Tried the monitor on another P.C and the monitor works
Tried the cable from monitor to P.C and this works
Tried in an old nvidia Ti4200 card that I know worked
The keyboard does'nt appear to be working when the pc is running because the lights don't come on when I press scroll lock or caps lock, the mouse lights up but now sure if its working and another thing I've noticed is that when I move about clicking even though I'd expect to hit some shortcut to a program making it start(if windows is running) I dont seem to get your usuall hard drive rumbling noise :( so I'm suspecting that windows is'nt booting up at all maybe a HD fault or that the VGA port on the board is'nt working.
Anything else I could try before a shop visit?

Power supply?

Fans are going and the front power light is on.

Do you have another power supply to try?

Was it ever overclocked? Try resetting to CMOS.

when you say another power supply do you mean another power block connector or a full PSU? I doubt the pc has been overclocked hes had it since new and he just does home pc stuff on there, as for resetting the cmos is that by changing a jumper on the board because I can't see the bios settings on the screen.

I was suggesting you try another complete power supply unit.

As for the reset, yes I was referring to the onboard jumper but that is in the case of overclocking. You could still try that but less likely the problem if it's not overclocked.

Put the HDD in your pc as a slave for now and backup the files.

Cheers I'll try his hd in his sons pc I don't want it doing anything strange on here ;) How would that work though will it be ok having drivers and system files on another HD and just plugging in? I'm also gonna have a shot at checking the power woth a volt tester just to confirm theres power to where it should be. The PC is a tiny and my bro has'nt got a clue what the board is so I'm gonna stay away from resetting at the mo but I'm guessing that if the HD works in another pc that the board is prob at fault, only other clues are that he thinks his daughter has been booting it up in safe mode to avoid putting his password in :D would that have any relevance?

Plug the drive in as a slave.

In your system, you keep your current drive as master and the OS boots up with your configuration. The slave drives' information will be accessible in "My Computer".

Cheers m8.