Lockup, then BOOTMGR MISSING, then won't boot from windows DVD

I came home to a frozen computer. Executed a hard reset after soft resets were ineffective. First got a disk read error, went into the BIOS and the BIOS had somehow swapped boot drives. Set the correct boot drive and got BOOTMGR MISSING error. Rebooted using windows installation DVD which is either loading excruciatingly slowly or not at all. I get the loading files message followed by the Windows splash screen, then the screen goes black and nothing. Fans are still running and on occasion I hear something or other spinning but no output other than a black screen. I never get to the repair/install windows screen from the DVD. I unplugged all my USB devices save my keyboard and mouse with the same results.

Any ideas?

EDIT: I'd like to add that I have other computers in the house, and if there is a simple fix that works around the DVD, I'm comfortable moving my boot SSD from the bad computer to another computer to fix it.

With mine I sometimes have to go into the bios 2 or 3 times to get the right boot order. It keeps changing on me & I don't know why but it eventually settles down.

My bios has two options in the boot menu. 1/ Boot order. 2/ Hard drive boot order. Both have to be configured.

Once I get the changes right I check once more to make sure.