go to controls in the menu, and click DEFAULT! if its correct all you keys will go to default keys, and console to, so the ~ works again ^_^ try it.
edit! if it doesnt work here are 2 more things!
1. your ~ doesnt work!
2. there is a file in your half-life directory, where all your key binding are in. custimize it and change it to ~ again.. let me see for the file name