Monitor suddenly "stopped working"

I couldn't see a thread about the same issue I have, so I signed up.

Before I start, I'd like to point out that I am not IT savvy (cars, trucks, household appliances - yes. computers - no), so please avoid IT jargon if possible.

The problem...
Our (Windows 7) computer has been working fine, nothing has been changed or added.
The computer was in use this morning and left unattended for a while and as usual had gone dormant.
When the mouse was wriggled to "wake it up", nothing happened - the monitor remained blank.

Eventually we tried the "universal fix" of turning it off & turning it back on, but it still did not work...
The "no signal" message popped up on the screen as it went off and when it was turned back on the "Windows was not closed correctly..." message briefly appeared (it does not do that now).

I'm using a lap top to send this (as I cannot use the desk top).

Any ideas?