When I turn on my compaq presario it starts the booting
Process and then goes straight to a black screen saying
BOOTMGR missing

This is a proprietary machine / software. You really need to get that answer from their site. I can answer in general how to get to boot, but it might not be a good move for the Compaq restore application or other settings on the drive.
Yep worked on 'em before, been a while ago. They are different. Not good or bad, just different.
