First of all, you need to get your phone into FASTBOOT. This is how to do it:
1. Remove the battery from your phone.
2. Replace the battery.
3. While holding [Volume -], press the power button once.
4. Keep holding [Volume -] until you see three little Androids skateboarding at the bottom of the screen.
Navigate using the Volume keys, and select using the power key.
You should see at the top of the screen, something like this:
Now, select "BOOTLOADER"
The word FASTBOOT should be replaced by HBOOT.
Navigate down to "CLEAR STORAGE" for a factory reset. I'm sorry, there's no way at this point to back up your data.
If that didn't work, please reply here... we will need to do a recovery