Windows Unexpected Shutdown

[Mike88]

I woke up my HTPC & was greeted by a message on the Windows 7 desktop. I also had the same message 2 weeks ago. It said:

Windows has recovered from an unexpected shutdown.
Windows can check online for a solution to the problem.
View problem details // Check for solution

Earlier in the day everything was OK. At that time Windows had a Defender update which I did. I also did a Malwarebytes scan & everything was OK. And then did a cold re-boot. When I had the same message 2 weeks ago, IIRC I also did a Windows Defender update & Malwarebytes scan & a cold reboot.

Then I noticed that a recording that took place just hours earlier was split into 2 parts with a few minutes missing in the middle. That same thing that happened 2 weeks ago & I think it was also the first recording after I did the update/scan. But everything since then was OK, until yesterday.

This time I FF to the end of the first part of the recording & got this message:
Video Error
Files needed to display video are not installed or are not working correctly. Restart Windows Media Center or restart the computer.

I looked in WMC7 at both of these corrupt recordings. Each portion was recorded with tuner #1 and had the same message.
The first part said: While recording (name): the computer lost power or experienced a temporary failure.
The second part said: Recording of (name): began late on 7/27/13 7:32:17 PM due to a temporary failure caused by either a system malfunction or a power loss and stopped on 7/27/13 8:10:00 PM.

The split recording from 7-15-2013 had the same message but with different dates & times.

When this happened 2 weeks ago I did look at the Events Logs but they're all cryptic to me. However I did see one that said:

ehshell.exe - Application Error
Application has generated an exception that could not be handled.
Process ID=0xf28 (3880), Thread ID=0xf68 (3994)

I Googled & searched but did not come up with anything meaningful. Most results related to not being able to start or run an app. But that's not my issue.

The HTPC is plugged into a UPS so that should be OK. Of course the PSU could be acting up. Or the mobo. Or something else.
How can I determine if it was a system malfunction or a power failure?