White Flash when I try to run Garry's Mod

Starting today, my Garry’s Mod refuses to start up. However, whenever I try to start Garry’s Mod with the option “-dxlevel xx” it starts up. I have cleaned out Garry’s Mod and reinstalled it. Nothing changed. Anyone have an idea as to why this is happening?

I am using Windows 7 Professional 64 Bit

Knowing your operating system is not really that useful. Knowing your hardware specs is.

CPU: AMD Athlon 64 X2 4000+ 2.1 GHZ
Mobo: Acer Aspire T180
GFX: PNY Verto nVidia GeForce 9600GT 512 MB

Please, tell me you’re not writing EXACTLY “-dxlevel xx”
Edit: AKA write “-dxlevel 90” or “-dxlevel 80”, not “xx”.

Yeah -dxlevel 95, 80 etc.