I switched on my PC this morning and went to do my weekly shopping while it booted up (made a cup of coffee actually).
When I returned it was sitting with the Bios Post on screen and not completing boot up.

Re-tried it a couple of times with no success.

I sat there thinking 'it was ok last night and the last thing I did was upload a few photos to Facebook'.

Aha...the truth dawned...I uploaded the photos from a flash card plugged into a USB Reader which was still plugged in.

Removed the flash card, rebooted and all was well

You're not alone    I have a HP server running Server 2003 R2 and regardless of Bios settings, it will always 'boot' from a USB drive if one is left plugged in.   Because rebooting a server is very disruptive in working hours, I normally do it remotely over the weekend - guess who left a 'stick' plugged in last weekend

M

I usually 'hang around' after hours to reboot the server. I don't trust either myself or the server to do it remotely these days.

I did once leave a floppy in with a driver on which stalled a reboot.

Should have left the thing plugged in , and done the shopping. !