Garry's Mod isn't working correctly after... steam update?

Hello everyone! I would like to report an error :confused: while in-game, i have noticed that on all servers, i get many many errors, along with p-models being black and purple squares, along with everything else. Most weapons are errors. I have talked to others, and i believe it is only for windows 64x systems, but i cant be sure. Please, someone verify this, and hopefully we can fix this problem. By the way, I have css and hl2 and have played on the server many times before with no problems.

P.S. I do not have beta of Garrys mod 13

I’m running Windows 7 on 64 bit and I have no problems, have you tried verifying the game cache of your copy of Garry’s Mod?
Have you tried deleting all your downloaded Addons, or even completely reinstall Garry’s Mod?

Have you ran the games (eg, CSS, HL2, TF2) atleast once (going to the main menu of them is fine) before since your last Steam installation/Operating system installation?