Dell Inspirion 13 , 5xxx series, built 2016, Win10 Home 64

Here's what happened yesterday. Any ideas?

1) Booted fine. Upon reboot, fan went to max, keyboard flashed on and off. This stopped then started again, repeat, repeat

2) Powered down

3) Upon restart, could not find bootable drive

4) Ran diagnostics - the full 2+ hours. Diagnostics said all hardware OK.

5) Tried to boot and again and could not find bootable drive.