M5040 keeps stopping

I bought an Inspiron M5040 for my son for Christmas and recently it has started stopping without any warning. It's not crashing or shutting down, but stopping completely, as if it's lost all power.

There don't seem to be any common factors with these incidents. For example, it can happen when you're using any program, it can happen when it's plugged in or not, it can happen when you have been using it for hours or just a few minutes (ie. I don't think it's overheating).

I have used the system recovery option to completely reinstall the machine but this hasn't made any difference. I have also run full diagnostics, but this hasn't revealed any problems. There are no incidents recorded in the Events section of the Diagnostics, so I can't find any clues as to what may be causing this problem in a laptop which is only three months old.

Does anyone have any suggestions?

Thanks!