How activate onboard gpu when dedicated gpu is broke (and removed)

Hello,

last time I had some problems with my HDD fan, after installation of TGPro my GPU went mad (shows coloured pattern und stops there, no reset possible). The ATI Radeon 4670 is removable, the dealer gravis wants 450 euros for an exchange! He gives the rest a value of 30 euros! I dont have the money for a new computer.

How can I activate the integrated onboard gpu, which is situated between HDD and the PCI port (Probably nvidia 9400, which should be sufficient for standard purposes)?

Happy Easter days, Andreas