What phone have you got, make and model? Because any possible fixes are very likely to be specific to the particular phone. Some devices you get them into fastboot mode, and then the recovery and/or firmware ROM can be reloaded via USB using a PC. On some phones you cannot use CWM to flash the stock firmware ROM, e.g. Oppo and Vivo, you have to reload the manufacturer's stock recovery, and you would do this via fastboot mode.