I would copy your Windows CD and try installing with that.
I would also do the following:
Reseat connectors for drives (HDD and CD/DVD).
After that, have a look at my guide to random reboots to see if that will help any.
Intel E6750...........PSN: ELBATROP
XFX nForce 650i Ultra
Patriot PC2-6400 8GB (4x2GB)
36GB WD Raptor
Samsung SyncMaster 931c
Samsung SyncMaster 750s
Windows 7 Home Premium 64