Hi there and welcome David
What now happens when you now try to start the computer?
it runs and only shows 1-3-4 diagnostic light with no beeps just the sound of the hard drive
ok, this is the diagnostics that reference "Another Failure has occurred" Its one of the ones that do not tell you whats actually wrong.
One thing, you said "something about trying to write to read only memory."
That points to the hard drive crashing, as it could not write to it.
But first power it off, disconnect computer open the computer and unplug and replug all components (hard drive, disk drive) to make sure all are seated.
Then connect power and try to turn it on
tell me if it then starts please.