Adistark :
Intel Core 2 Quad CPU Q6600 2.40GHz
4096MB RAM
Gigabyte G31M-S2L
Geforce 9800 GTX+
Your new PSU is more powerful than the system requirements. Right now, the best solution is to test that GTX in another system to be sure it still works as before (you can try to re-seat the card in its PCI-E slot). I just hope that your old PSU didn't take with it either the motherboard, or the GPU...
If you are not using your HDD's in RAID, try to go into BIOS, set it to default and see if it changes anything (also, uninstall/reinstall drivers for the motherboard and do the same for the graphics card).