I'm a bit confused. So you said the screen is black even while in hboot?
And you are cdma, right? S-on or s-off? And to get into fastboot usb i think it is more like, power off your phone completely, if you were using sense 3.6 rom i guess it is a good idea to remove the battery for a sec in case fast boot was enabled in settings, then pwr+voldwn, wait a moment, pwr again and now you should be on fastboot.
Then on pc make sure you have installed all the required drivers for your phone and download fastboot. Connect your phone to the pc. Copy a recovery.img on the folder on your pc where fastboot executable is located. Then shift + right click on an empty space in that folder and create a terminal (cmd) there. Run fastboot flash recovery.img. then try to boot into recovery again. So shut down your phone again. Then pwr + voldwn. Again voldwn and now it should boot into recovery. You may also use 'fastboot reboot recovery' from fastboot instead of this i guess. If it doesnt work do fastboot boot recovery.img. If you are s-off you can just flash a ruu if it didn't work, but you will lose root ofcourse. If s-on you need to relock bootloader in fastbbot mode with 'fastboot oem lock' and then flash the ruu. I dont have time to find a ruu for you, so you better google for it yourself. Make sure to choose the appropriate ruu for your phone. To flash the ruu you just open the downloaded ruu.exe file and it will start flashind. It will take time and will tell you when it is done. If you are s-off i am not sure if you need to relock the bootloader but i guess you should not. If you are on a custom hboot(only possible if you are s-off), please no way lock your bootloader it will hardbrick it!
You may send me a pm. And i will do what i can to help you.
---------- Post added at 02:44 AM ---------- Previous post was at 02:11 AM ----------
And if you are not s-off i would reccommend you to go s-off after you have fixed this issue. Wire trick is the easiest way to gain s-off imho. Just go to this page and read the info on how to do this. I got s-off on my second try. It must be timed correctly. If anything goes wrong read the troubleshooting section. http://unlimited.io/juopunutbear.htm
And as always, if you need any help feel free to pm me.