Well...honestly, i'm not sure what to tell you...except, that I heard that you could just rename your garry'smod folder(s) -- Both of them -- and just see what happens.
It will get rid of your addons, plugins, scripts, maps, etc...even all of those errors.I belive i've had this exact problem before...not sure what I did - But I'm no longer having that general problem. So mabye, you just need to look up the answer online just for the rest of the details. And i'm just saying, it might aswell be a resolution problem if it's got a black screen -- even if you can hear sounds, too. I know you've also been crashing lately but I can tell you resetting the GMod folder's name is probably one of the best ways to fix it.