Tips for resolving issues! [Please Read]

Remove all addons. Don’t necessarily delete them, just move them into another folder inside addons called ‘archive’ or something. If this solves your problem, then one by one move each addon back until the problem occurs.

In Steam, right click the game you are having troubles with, select properties, then ‘Set Launch options’ in the box, add -sw
This will make the game start in windowed mode. If this resolves your problem, try re configuring your graphics settings

If your game loads to the main menu, select options, the keyboard tab ( should already be there) then advanced. Check “Enable Developers Console” Press the ~ key and look for any errors. If you can join a game without crashing to desktop, it is recommended you look in the developer console for errors. most likely the reason will be there

Backup your addons, and re-install garrysmod. Make sure it boots properly first before replacing the addons!

Make sure you have the following installed (not necessary, but will help fix the purple checkerboard ( missing texture) and red errors(missing models))

If you have anything to add to this, or any revisions please post a reply, thank you!

Fresh re-install of Garry’s Mod could go on there.

Got it on there. Thank you =)

Not to bum you out or anything, but most (if not all) of this is covered in the FAQ in the Sticky at the top of the page.

Yet somehow 90% of the questions are about this.