Ensure that you have the latest BIOS for your system
Ensure that you have ALL Windows Updates
Ensure that you have ALL updated, Win8.1 compatible drivers for your system
This includes all Intel updates and Bluetooth updates
Have you disabled all non-Windows shell extensions to see if that stops the problem?
If so, did it stop the problem?
Just because a system used to work fine doesn't mean that it will continue to work fine.
With overheating problems, dust accumulates, hair gets sucked into the fans, thermal compound may dry out, components get fatigued with heat/stress over time, fans stop working, etc.
Why did you decide to update to 8? Was it because of problems with 7? If so, were the problems the same?
I saw an explorer.exe error in the log blamed on msxml6.dll This is a part of the Core XML Services which are a part of Windows.
As such, the Windows Updates are the first thing to fix.
Next would be the disabling of all non-Windows shell extensions
Next would be this:
Then please run the following DISM commands to see if there's any problems with the system (from an elevated (Run as administrator) Command Prompt). Press Enter after each one:
Code:
Dism /Online /Cleanup-Image /ScanHealth
Code:
Dism /Online /Cleanup-Image /CheckHealth
If the problem is fixable, you can use this command to repair it (from an elevated (Run as administrator) Command Prompt). Press Enter after typing it:
Code:
Dism /Online /Cleanup-Image /RestoreHealth
From this article:
Repair a Windows Image
You can also run sfc.exe /scannow from an elevated (Run as administrator) Command Prompt to check for further corruption.
And next would be a REFRESH of the OS.
Good luck!