Hi Trevor and welcome to the forum.
So once the computer has fully booted the monitor is fine, correct?
If that is right thenm the problem lies in the BIOS graphics settings somewhere. Lets start at the beginning though and from what you said it takes a while to boot as it 's looking for the various devices so I would advise disabling in the BIOS anything like the floppy drive, IDE, parallel port etc. It willl make the system faster to boot and release resources. Can you list your hardware too please?