This happened after I downloaded Steam and logged in on a different computer, not sure if it’s related but it probably is.
So I had to re-download ALL of my Steam games onto this computer (the orignial one, different one to the above mentioned), which had never happened to me before. After a few days of downloading, I finally got to play GMod. But none of my addons were installed. This probably means I’ll need to re-download all of THEM again, (confirm?) which is really fucking annoying.
Anyway, I just wanted to know WHY this happened.