hl2. exe error, cant find solution

i recently bought garrys mod and i have had counter strike source and half life 2 for a while. A while ago when i tried to start up CSS an error came up saying…

“hl2. ece has encountered a problem and needs to close.
We are sorry for the inconvenience.”

same thing for garrys mod

half life 2 will start up, but the other two wont.

ill be happy to post more information.