I have been having this problem for some time and tried all the fixes listed on this and other forums that relate to using the DVD repair and command prompt repair solutions.
None of them worked!
I discovered my solution in the BIOS settings. The hard disc boot order was incorrect. For some reason I was unable to change this setting using my wireless keyboard so bought a cheap USB keyboard. I then selected the correct drive to boot first and all is fixed!
Still not sure how the boot order got changed though. It was set correctly when I built the machine but at least it now works without the DVD in the drive again