When asking for help it's very helpful to provide the error message to your question.
Usually it can be found in the console after scrolling up a bit(pgup or mwheel).

This error occurs when quake tries to allocate more memory than it's allowed to use. (Happens on big maps like b0 for example)
Solution: Increase com_hunkMegs.

You miss file(s) needed to connect to the server. The server may use a different version than yours. For example: current version is 1.48 but a server is running on 1.47.
Solution: Get the needed file.

Quake is designed for the US-keyboard layout. Using a different layout may complicate binding some keys.
Solution: Go to the controls section and bind the key to retrieve it's code.(cnq3 only?)