EDIT: I changed HL2 to HL2_old, and for some reason it works again.
I haven't quite been able to find people with this problem or how to fix it. Amnesia runs perfectly fine for me, and my graphics card is a GeForce GT 240 (Nvidia), which is a more than sufficient card, and I run more detailed games at high settings with ease.
The problem is this: I downloaded the level editor for amnesia. Yesterday it ran fine, (aside from the program window being insanely large relative to my 1024x768 screen*), but out of nowhere whenever I try starting up the level editor I get a black screen and then a message saying "Fatal Error: Renderer #0 could not be initialized! Make sure your graphic card drivers are up to date. Check log file for more information".
Meanwhile, the model and particle editors work just fine.
----------
1. That's still an issue with me