My friends gmod has been severly broken for months

so one day my friends (friend A, Friend B and Friend C) where playing TTT. Friend C brought their friend along and they got into an argument about rdm and friend C’s friend infected A with what can only be described as a “Gmod virus” I’m not sure how it happened I wasn’t there and my friends cant really remember.A’s game then started to act strange. his camera froze. he could not look up or down. and his sensitivity was really fast. he had to go into the console and make it 0.004. is gmod is now unplayable but it doesn’t stop there. he then went to friend B’s house and use his computer to log onto his account and launch gmod. he still had the problem and then friend B has the problem on his account. they have done many things to try to fix it. they tried to uninstall the game validate the files delete the Lua folder the config folder and they unsubed to their workshop items. has the happened to anyone else? how can they fix it without having to buy a new copy of gmod?

Tell them to turn off Steam Cloud Sync for GMod, delete their garrysmod folder, and entirely reinstall.