As you are able to boot into fastboot mode, you can use this to flash your ROM. Details can be found at our sister-site, take a look e.g. at I can FastBoot my device. How can I reinstall an Android image to it?.
However, this requires to have compatible images, as fastboot flashes single partitions (and not full ROMs, at least to my knowledge). If you don't have such, and don't know how to convert your ROM into this format, on Android Enthusiasts you can find another useful ressource: Where can I find stock or custom ROMs for my Android device? This might help you finding a compatible ROM. A question like "How can I make my ROM image compatible with fastboot?", including the facts from your above question, would be on-topic there as well, just in case.
For more information on fastboot, you can refer to the fastboot tag-wiki at the mentioned sister-site.