right click on the game's shortcut and select "start this program in safe mode" it will boot up in 16bit and 640x480 resolution ans possiley windowed mode, but you will atleast be able to see the menu and can there change the resolution to something of your likeing.
go into your cod4 profile, go into the config, delete the config_mp and start it up cod4, all your settings will reset but it will fix it, and yes you WILL have your rank still.
C:\Program Files\Activision\Call of Duty 4 - Modern Warfare\players\profiles\(your profile name) and delete config_mp, then restart COD4... and don't set the Res so high next time