weird graphics/power problem

Please can someone figure out what is wrong with my system!

The signal to the monitor was being lost now again (mainly when trying to boot into Windows)
Now I have nothing being displayed on the monitor at all. The graphics card is a ATI 9800se All in wonder (AGP)
So I got hold of an old Matrox VGA Card (AGP again) and I still have the same problem.

Also the computer seems to have problems switching on (does not always respond when you hit the power button). The reset button does not work, and the computer can not be switched off from the power button!

So at the moment I think it may be a problem with the motherboard but it is a bit difficult to tell. The case fan, PSU fan, CPU fan and graphics fan all have power going to them though.

Is there anything else I can check/test to fix the problem?
Is it worth trying to get hold of a PCI Graphics card?
Thanks

Spec:
AMD XP3000+ CPU
MSI K8N Neo Motherboard
ATI 9800se All-in-wonder grapics card
2x512MB RAM (not sure of the make)
Samsung 160GB IDE Hard drive

What's your Power Supply?

it is an Akasa paxpower 460W - about 3-4 years old.
is there an easy way to check the voltages?

You need a Multimeter, which makes the easier solution to try a different PSU if possible. The PSU is a possible culprit, but the motherboard is also a contender. Other parts seem less likely.

The thing is that if you have a bad PSU then it might have taken something else down with it. And you shouldn't try the PSU in another machine for that reason. But trying another PSU in your machine would clarify whether the problem lays there.

thanks for the reply. I have managed to check the voltages on my PSU - and they all seem to be fine (about 2% out) - I manged to test 2 different molex connectors and the main 20 pin block.
So I guess it is the motherboard which is faulty.