I did some more checking, and two additional items, memory and corruption in Windows.
Several hits for the PROCESS_HAS_LOCKED_PAGES error when shutting down or opening full window app.
Considering the many "abrupt" shutdowns potentially two items stick out (1) corruption on the hard drive (2) corruption in Windows. Both of these suggest a "clean" reinstall (reformat the hard drive and reinstall). I'm sure neither one of these would make you happy if it turns out to be the problem.
Do you have a spare hard drive that you could install and then install Windows on that? I know its a hassle but would at least eliminate these as potentials.