gmod crashes when I create single player sandbox mode

Unable to play Sandbox
'ma try to make this short:
Let’s say i am one of these players who play TTT and Prop Hunt a lot, but i want to play Sandox mode sometimes, so i select “sandbox mode”, Open up Single Player, Select a map (doesn’t matter which one) wait for it to load and… here’s the problem.
It loads like it always does, a bit slow, enough for you to go the kitchen and make yourself a sandwitch before it loads, so the game loads… it comes to “Initializing game data” it stops loading (the bar doesn’t fill up) i wait patiently, the it just goes poof, back to the desktop, no warnings, no error pop-ups, it’s as if you ALT+F4’ed, just… quits…
The first time i thought "Hmm… must’ve been an error with the map, i try another one.
AND THE SAME THING HAPPENS AGAIN, AND AGAIN, AND AGAIN! (i used Caps-Lock so you know i’m serious)
Now, what the hell? Am i FORBIDDEN to play sandbox mode? it’s there 60% of GMod’s fun is, but it just doesn’t want to let me play it…

I heard from some people that it’s because of the updates, that “Garry fixes things that breaks other things” etc.

I’m not sure, it always seemed to work for me, but recently it just started “throwing me out”

I have tried verifying game cache, re-enabling add-ons, deleting all add-ons, and of course…
reinstalling the game, so far… nothing worked for me, and here is my question:

Do you know a solution to this “crash”?

This is caused by you having too much addons resulting in them conflicting with each other. Uninstall or disable all your addons and try again.

I have friends who have about 800 mods and not have problems.
500 I have this error happens because the computer is bad
or some mods will conflict?

Probably both. 500 or 800 is way too much.