Why did my Linux Mint system crash? - update

[joe at actionline.com]

So I shut the system down for a while,
and after about an hour, I tried it again
and it started up fine.

It wasn't particularly hot (it's a Lenovo net-top)
but after cooling down, it started up okay ...
enough so that I could back up all my data.

So what can I do to test the HD and other parts
of the system to see what the problem might be?