Over heated graphics card on HP Pavilion DV900?

My Sister’s HP Pavilion DV9500 has developed a fault. She said it got very hot. The screen was patchy blotches of red on blue and the modem slowed down.

I went into safe mode and reinstalled Vista, you now can see the screen but if you try open a picture it goes back to its old problem. The modem – Motorola SMS6 will no longer connect either wireless or directly to the internet.

I have done the Microsoft memory test which it passed. So I am starting to think the graphics card is a Geforce 8600M GS, has overheated and developed a fault and damaged the modem as well, unless this uses the memory from this card?

How do I find out for sure the graphics card and other parts are now faulty and it is not some other problem which can be cheaply fixed?

Many thanks