Start up troubles.

Today, I decided to re-install garrys mod from steam. After it had finished downloading and I clicked play and it wouldn’t start up, it just showed a message (sorry, forgot it) and shut down garrys mod. So I decided to delete all the files in my steamapps/playername/garrysmod and redownload. After that it started to work fine but then came up with “hl2.exe has stopped working” and now just keeps saying that. I’m not sure if it’s missing a file or something.