The default path for that folder is C:\Program Files\Activision\Call of Duty 4 - Modern Warfare\players\profiles. If you want to save your online profile and save games, browse the game folder and then open the players and profiles folders. If you have the Steam version of the game right-click Call of Duty 4: Modern Warfare > Click Properties > Click 'Local Files' tab > Click 'Verify Integrity of game cache.' Once the verification is complete Steam may download missing game content. Make sure that you do not install any third party maps/mods/skins of any type. Uninstall the game, delete the game folder, and then reinstall the game and the patches. If you can't find a solution here go to the support page at activision, if they haven't seen your problem before then post a question