I have a 2011 iMac, and was having no problems using Bootcamp to dual boot the 8.1 dev preview and OSX.
However after doing the update in the Windows Store to the release 8.1 version (after making sure proper drivers were installed) my computer works perfectly fine, except every now and then it randomly starts shutting itself down. It doesn't just turn off, it shows the 'Shutting Down..' screen and goes through proper procedure, but I never tell it to.
I tried reinstalling 8.1 directly (using 8.1 ISO ), but it still has the same issue. I've seen a few similar problems while trying to Google the problem but no real answers as to how to fix it.
Any help would be great, thanks in advance.