I have an old LG R500 laptop running Wind0ws 8.1 Update 1 and it recently started powering off during boot up… very bad. The machine would boot in SAFE MODE and SAFE MODE WITH NETWORKING but not to the full operating system. At least this told me that the core hardware (like the harddrive) was functional.
For some reason Microsoft has apparently removed LAST KNOWN GOOD as a boot option and that I dearly miss.
After trying several different SYSTEM RESTORE dates, running SFC /SCANNOW (but not finding any problems), I gave up and tried REFRESH YOUR PC (which basically replaces all of the Windows 8.1 system files and re-registers .DLL’s, but does not affect most installed programs or your data). Unfortunately that failed… not good.
From experience I know that odd problems like this are often caused by video problems, soooo, I booted into SAFE MODE, used DEVICE MANAGER to remove (and delete the driver data for) the NVidia 8600M GS video card… then I rebooted, it crashed, I booted it again and BINGO… all was well. I then used Windows Update to re-install the driver and again… all was well.