Need to know a few things:
1. Cricket or MetroPCS?
2. What build of CM7 are you trying to flash?
3. How long did you wait on the Ascend splash screen before doing anything? The first boot can take several minutes.
4. Are you saying you didn't make a nandroid backup before flashing CM7? If so, you can always download the files to flash the phone back to stock, and you will find that thread in the All Things Root section, which is at the top of this forum section.