WideGlide wrote:

This never happened before. So you mean a poor
keyboard cable connection will cause a computer to be totally disabled?

The flashing ? mark means it can't find a drive with a valid operating
system. Make sure your Startup Disk control panel is still set to the
drive from which you've been booting. And make sure you have up to date
backups for whatever data you would unappreciate losing that is on the
drive in question.

The reseating of kybd and other cables and the successful boot might be
coincidental. You might also want to rreseat the connector to the drive
with the OS on it.

--
ha