Sigh. You are bricked. Not an easy fix. You have options, though.:
- Flash the stock ROM via PC, and see if it is a soft brick. If that works, you'll be at step 1 again, but that's better than a unusable phone. This is assuming you can aaccess a mode to flash ROMS via PC.
1.5. Make a USB jig (look up one, it varies on device). Use it, and it will make option 1 easier.
1.7. Take apart your phone, grab the hard drive, load it into anything that will take it(again, look it up, I know someone asked about it here a while back) and grab the backup, then do option 1.
Keep trying to get it to boot up, and keep it charged. You may just get lucky.
Take it to the manufacturer, and say it just stopped working. Provided they don't work out what you did, it''ll be at stock again.
Throw it in a bin :(
Some of those may be crazy, but there is often little available for bricked devices. I have lost two devices like this.