Crashing within minutes of joining Lobbies

I have recently begun playing in tf2 lobbies via tf2lobby.com, but I cannot have any fun whatsoever because of the fact that the game crashes within minutes of joining every time.

I almost never get crashes when playing in pub matches, and on the few occasions that it happens, it displays a message of "hl2.exe has stopped working".

When I play in a lobby, though, the game crashes without any error message or warning. I have tried ~5 different lobbies in both HL and 6v6 format and none of them have worked. I have a custom HUD and a few custom skins installed but that is it... I'm not sure what's wrong - any and all help is appreciated.