It kinda sounds like a jumper setting gone wrong on the DVD burner. Double check to make sure that it is one either Cable Select or Master. In fact, I would try both to make sure.
Also, make sure that your DVD burner is showing up in the boot order in BIOS.
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