download fastboot and unzip to c:\fastboot, download GNM recovery, copy image file to c:\fastboot, make sure you have all the android drivers for the phone installed, then connect your phone, open your device manager and look to see if its showing up as a fastboot device, if so then open command prompt, navigate to c:\fastboot and run this command:
fastboot flash recovery yourrecovery.img
make sure you change the yourrecovery.img to the actual case sensitive name of the recovery image, something like GNM-optm-somethingsomething.img
this will flash a recovery image to your phone, you can then enter recovery and either restore a backup you made or flash a new rom hope this helps