Ultima X01 Shutdowns

I bought an Ultima X01 some time ago, it performs well and works correctly, form the most part.
The thing being that if my computer will be on for most of the day, it will randomly shutdown.

If the PC is turned on for longer than 6 hours-ish it will eventually randomly shutdown, closing my work or game, this is frustrating as I can lose anything I did within an application.
This happens no-matter if I game, or do simple web browsing, or do nothing and just leave it running on the windows desktop.
The PC is not overclocked currently, and I do monitor my temps, both on my GPU and CPU, which are 20-30 degrees Celsius when idle/web browsing, so this cant be a temperature issue.
For example I can be typing something up or playing a game, when suddenly there is a click, and the lights on the pc turn off, along with the PC, after the shutdown windows doesn't report any issues, its as if I shut it down myself.

Is there any reason this could be happening?
If I wont find a reason why this is happening I will send the PC off for repairs, but I want to try fixing it myself if possible.

Thanks in advance.

I would check a number of things before getting it repaired....

1. Unplug all external devices except the mouse, monitor, and keyboard and see whether it still shuts down.

2. Check that all cards are properly seated (especially the RAM cards). Pop them out and back in. Also check that all connectors are fully home.

3. Run chkdsk /r on all your hard drives/partitions - I'd advise a full backup before you do this though.

4. Donwload Memtest from https://www.memtest86.com/, select either the ISO or USB image, extract the image file from the downloaded archive and burn that to a CD or flash drive as appropriate. Then boot that media and Memtest will start running. I always let it run overnight, it does take a while to complete one iteration of all the tests.

Others may have other tests/checks you can try....

Check the event logs before shutdown, should tell you weather it’s software or hardware related. You don’t mention your temps when under load?