GMOD crashing or being dumb?

Well, every now and then when I play gmod and I am playing on a server it will freeze then when I ctr+alt+delete, it wont say it crashed, Their will only be a black rectangle at the top left of my screen and it wont let me click anywhere but my task manager and the start menu bar at the bottom. I try clicking the gmod icon at the bottom as well, but it dosn’t open anything.
I have a…
GEForce GTX 560 TI
8 GB of ballistics ram
AMD Athlon 4 core proccessor
I dont lag on gmod, it just does what it does sometimes.
Please someone tell me how to fix this (crashing) or whatever it is. It annoys me and I cant play the game I am playing. {perp} its only me this happens to. My friends crash, but not like mine.

Please read the big ass notice that says that this is not the section for support.