I tried the beta for 8.1 and well, it marked my program files as a malicious folder somehow and after that, got bombarded by a ton of memory access and werfault errors (DLLHost, Taskhost) to which I ended up with a black screen. The mouse was working (it was effectively if explorer.exe crashed except task manager would not load to let me execute it) and after rebooting, instantly blocked them all again on logging on and back to square one.
So, tried system restore and well, got blocked by it with that as well but! Safe Mode finally prevailed and I was able to remove it.
(If you need to get there, Shift+F8 (hold shift and spam F8 as per usual) to trigger the recovery mode then "See Advanced repair options" button followed by the "Troubleshoot button" then "Advanced Start-up options" then "Reset now" and the good old advanced boot option menu will pop up while booting (Safe Mode, Safe Mode with Networking, Safe Mode with Prompt, Disable Signature Enforcement etc)