Nexus 5 unable to reflash
Issues like this this are often corrected by returning to a "known good configuration" before processing additional changes.

I would suggest returning to the current official Google firmware via fastboot, then verify the device is booting and operating properly, then you can flash custom recovery and install a third party ROM such as CyanogenMod.

Instructions and factory images with flashing scripts are available directly from Google at their Factory Images for Nexus Devices page.