Hardware or Software?
 

I have recently installed a new operating system on a computer I haven't used before. It hangs occasionally (every couple of days), neither the keyboard nor mouse will work. I haven't found any key combination that will escape from it - perhaps not possible in that situation anyway.

I have looked in /var/log/syslog, but don't know what I'm looking for. Is there anything that would indicate whether the problem was software or hardware?

I need to know whether there is something wrong with the computer before I commit to using it.

Hi Chris...

What is the brand and model (and model number) of the system and is it a desktop or laptop? One thing you can do for starters is to run Memtest86+ for a few hours (at least 30 passes) and see if any errors come up.

If you would, please post a copy of the log so folks can go through it, if they wish.

Absolutely. :)

Regards...

Is that a couple of days continuous running, or do you shutdown/hibernate during that period ?. If the former its likely hardware.
I suspect by now Canonical has fully committed to systemd, so journalctl should work for logs. Try this to see the last 20 lines from your previous boot to see if anything interesting occurred.

I switch it on in the morning and leave it on most of the day.
It gave this response: "Specifying boot ID has no effect, no persistent journal was found"

Seriously ?.
No wonder I gave up on Ubuntu years ago.