This all started when I started having trouble with my video card...while in a 3-D game I started getting a blue screen "NV4_DISP" error...after many hours reading online I came to the conclusion that my video card was going bad....I ordered and installed a new one(8800GTX)...when I turned on the computer I could again read the boot up screens up until I started getting another error "missing or corrupted file \windows\system32\config\system"...

I then decided to do a reinstall of the OS, Win XP MCE 2005, using the reinstallation DVD shipped with my machine...
I then changed the boot order in BIOS to boot to the onboard CD drive 1st and kept getting "selected boot device unavailable"....I have tried a new reinstallation DVD from Dell and a new DVD drive....still nothing.....I have run the diagnostic program from the resources CD and everythig passes.......

If I boot up with the DVD in the drive I get a black screen error msg "error loading operating system"

If I boot up with the DVD in the drive , hit f12 and select boot from cd drive I get error message "selected boot device unavailable"