For some reason lately, when booting up or restarting my PC and logging in (with a picture password) the Metro Start screen that comes up sometimes randomly freezes/locks up. I can still move my mouse but the tiles aren't clickable at all nor do the live tiles change. Any buttons on the Metro UI don't respond either and the charms bar doesn't show up. It is as if the screen is completely frozen except for my mouse. There isn't anything I can do except pressing Ctrl+Alt+Del and doing a restart. Choosing to log off instead and logging in again still shows the Metro Start screen in a locked condition.

I haven't made any changes prior to this issue except disabling the option for Windows to bring me to the Desktop immediately after a boot.
A sfc /scannow doesn't show any corruption.

This issue happens randomly and I have no idea what triggers it, so I can't say for sure if it also occurs in Safe Mode or on another user account.

I'm running Windows 8.1 Pro 64bit with Media Center
i5-3570K (stock) CPU and a GTX 660Ti GPU with latest drivers
8 GB RAM and 1 TB HDD

EDIT: Just noticed that I can press the Windows key instead of Ctrl+Alt+Del. When doing that, the screen blinks a bit and it brings me to the Desktop. An error shows up in my events saying that Explorer.exe has crashed. Here's the log:

The program Explorer.EXE, version 6.3.9600.17284 is not responding to Windows and has been shut down.
Proces-id: 580
Starttijd: 01cff3ed53c30a9e
Eindtijd: 15
Toepassingspad: C:\WINDOWS\Explorer.EXE
Rapport-id: 9963ff96-5fe0-11e4-becc-bc5ff44ab185
Volledige pakketnaam met fout:
Relatieve toepassings-id van pakket met fout:

There is no dmp file.

Any help?