Random shutdown, domain user, Windows 7 32-bit.

Hi everyone, I'd like to run something past you all if I may?

I work in the IT Support department of a Further Education College in the UK and for the past few months we've experienced a weird problem with a specific user's PC in that it will randomly shutdown.
It's a real head-scratcher and I would love some input from some fresh eyes!

Here's the scenario:
She logs in on a morning fine and can be logged in for hours before her computer goes through its shutdown process, displaying the default Windows "Shutting Down" screen with the pretty flowers to the right.
She boots it back up and can be working away for a few minutes and it will shutdown again; the next time a few minutes or hours. It's very random!

Here's what I've done so far:
- Checked the Event Viewer and found nothing untoward.
- Changed the RAM - no change.
- Changed the hard drive - no change.
- Changed her WHOLE PC for a new one - no change.
- Changed her PC name (in case it had something to do with that) - no change.
- We did have some software called Impero installed on her PC which was capable of taking remote control, starting the PC up, shutting it down etc etc so I removed this - no change.
- I read on a gaming forum that some people have experienced this problem with certain keyboard. In her case she was using an Apple keyboard so I changed this for a standard Microsoft keyboard - no change.

I thought maybe it was something to do with her network account and thought about changing her username in case she was being targeted somehow - she uses a laptop on the same network, same username etc and this works fine and doesn't shut down!?

A colleague of mine checked the Event logs and found something relating to the shutdown in that it was a command from Windows. When he sends me the information I will share it. Until then though, any ideas on the cause or a resolution would be greatly received :) Its driving me round the twist!

Thanks in advance