[Windows 8.1] Black screen after updating nvlddmkm.sys file

I currently own an Alienware X51 (8Gb RAM GTX 660 OEM i7-3770 Windows 8.1).

Last night I followed the instructions of this guide to fix the nvlddmkm error, but the screen went black some seconds after booting up my computer and the mouse cursor kept flashing and jumping to the center every 4 seconds; I couldn't even log in.

I tried to set the integrated graphics card as the primary gpu in the BIOS. Furthermore, after many tries of going into Safe Mode, the Alienware icon and settings—at startup—stopped showing up completely. Now there's no signal on my monitor until the Power-On Self-Test is done (before the beep) and the black screen persists.

Could you please help me find a solution for this issue?

Thanks in advance. :)