Hi: symptoms (when they occur) under Win 8.1:
Safe Mode: Desktop crashes, taskbar unresponsive, no charms bar. Can launch task manager with CTRL SHIFT ESC.

Windows 8 seemed ok- but that's what I've seen as soon as I updated to Win 8.1 and repeatedly struggled with (more below). Presently my Win 8.1 is functional. (See final conclusions as to how I've managed this).

Today I believe I have identified one culprit:
Advanced Uninstaller Pro 11.3
- listed as compatible on MS's compatibility check site.

Installing it under 8.1 was fine, normal mode fine. But got the above symptoms on checking Safe Mode. (Prior to installing Safe Mode was ok - I'm looking for this particular symptom).
Restart to normal mode: similar symptoms. Uninstalled the program.
Restart to normal mode: same symptoms.
Used restore point set just before installing program.
Normal Mode Ok.

1. MS Compatibility site may list it as compatible 'cos people haven't used safe mode. (If anyone encountered the problem above, it could be when they used safe mode a very long time after installing it).
2. Uninstalling wasn't adequate. (I think it did warn of leftovers to be manually removed).

For over a month I've been struggling to build a configuration similar to what I had with Win 7, using programs that worked well. Compatibility check showed almost no problems.

I've repeatedly encountered the above symptoms; the first time was after having installed many programs, and then thought to check Safe Mode.

At first using autoruns, it seemed associated with certain filters in one section, 3rd from end. Disabling those, expecially the optional ones Zoom player offers and Xvid, and a couple of Apowersoft ones, removed the problem.

But it eventually became clear there was something more.

I built a temporary Win 8 (not 8.1) config with about 100 programs installed; fine. Upgraded to Win 8.1: BANG. Symptoms as above. That within a day. This convinces me there is a vulnerability in 8.1 not present in 8.

I restored a disk image of Win 8.1 with many programs installed, but in which Safe Mode and Normal Mode failed as above. I uninstalled all programs, hoping to identify one as a culprit. No change. That is consistent with my finding for this program.

In Win8.1 if you are intended to install more than, say, 10 or 15 programs and do lots of configuration (i.e. takes a long time to set up, then:
1. use manual restore points frequently.
2. use disk images frequently (I prefer differential but incremental saves space)
3. Retest Safe Mode after installing 3 or 4 programs.

Hmm. Never had to be so careful with any other version.

How could one identify why explorer is not responding given the above symptoms?

HP G60 214EM laptop, 32 bit O/S