We started having several PCs in our district reboot without warning too. Most people would tell me that they rebooted while they were on break or while the PC was idle. Looking at the logs we found event 6008's too. PSU would be a good guess but this problem requires a little bit more of troubleshooting. In our case we found that the PCs weren't rebooting but were instead blue screening. Make sure you go to Advanced System settings >> Advanced tab >> Startup and Recovery. Uncheck automatically restart and change the debugging information to Small Dump. We pushed out a reg key so that all of our district PCs would freeze on BSOD. We found by doing this that the problem was more widespread. Doing some troubleshooting on the BSOD led us to this tech net article: https://social.technet.microsoft.com/Forums/en-US/53b5a73e-b1f4-4361-9c8a-206f6a67f70f/bsod-csrssexe-crash-sxsdll-cause?forum=w7itprogeneral
Which then led us to this hotfix: support.microsoft.com/kb/2675806/en-us
While the description was similar to what we were seeing it wasn't exactly the same. With more PC BSOD'ing by the day we decided to push the hotfix out and our PCs are no longer BSOD'ing. From what I can tell either a Windows Update came through and broke something or it was an update to .net. We were in the same situation too. I knew it wasn't a hardware problem because multiple PCs were effected and they were using a different image. This may not be your exact problem but the above has good troubleshooting steps.
