To enable the console create a shortcut that appends +seta com_allowConsole "1" to Quake 4 and press ' (UK key below ESC) or CTRL+ ALT+ ~ (US Keyboards) or CTRL+ALT+ ' (UK Keyboards)

Quake4.exe +seta com_allowConsole "1"

or use the following to skip intro animations / movies and enable the console

Quake4.exe +seta com_allowConsole "1" +disconnect