This issue isn't exclusive to Garry's Mod and is happening to multiple other games with Steam Workshop support, such as Left 4 Dead 2. There is a trending issue with Garry's Mod when your mods from workshop will stop working and will no longer load in-game, and in main menu addon list, it will say 'Nothing Found'. Please consult your Touch Pad User Manual for information on how to disable the Palm Protection. To fix your problem, you must either disable this feature in your Touch Pad software, or buy a proper PC mouse to play the game the intended way. This feature exists to avoid accidental clicks while typing on your Laptop. There's a feature called 'Palm Protection' that disables your Touch Pad completely when a key is pressed on the keyboard. The actual cause of this problem is your Touch Pad's software. Please note that this is not officially supported way of playing Garry's Mod.
This problem is most likely caused by you using a Laptop Touch Pad in order to play Garry's Mod. I cannot click on anything in Garry's Mod while playing This article will describe most common problems with Garry's Mod and how to solve them.
