This is starting to affect my GMod as well. When I'm in fullscreen, it eventually connects to the server, but it freezes at the camera view of spawn before the menu shows up, forcing me to have to restart my computer (I have dual monitors so that may be part of it)
When windowed, it simply freezes on Sending Client Info/Have fun!, and never changes.
I recently cleared my cache folders and that didn't seem to help. It used to happen very rarely, but this past week I haven't been able to connect at all.