This could be due to a corrupt firmware. I should re-download the firmware to start with (I hope one day Adtran provide MD5 or SHA checksums to save us from problems like this). Then you will need to reset the router and place it into Bootstrap mode:
Power off the router. Power it on and imediately press the Reset button and hold it depressed. Eventually the STAT light will stop flashing and will remain alight. You should be able to access the router on IP address 10.10.10.1. Set up a static IP on your PC to be able to connect to the router using telnet. Then get a TFTP server running on your local PC and make sure that it is not being blocked by the PC's firewall.
Once connected to the router see if you can list the filesystem:
Bootstrap# show flash
If you can see the firmware you uploaded, try to delete it:
Bootstrap# erase file_name.biz
Alternatively, you can erase everything on the Flash drive:
Bootstrap# erase file-system
Note: If you do not have a backup of your configuration and want to try to back it up BEFORE you delete the whole filesystem, you can try:
Bootstrap# startup-config tftp
Address of remotehost? 10.10.10.10 (or whatever your TFTP server is running on)
Destination filename? backup_config
Then proceed to upload the fresh copy of the firwmare you have just downloaded.
Bootstrap# copy tftp flash
Address of remotehost? 10.10.10.10
Source filename? file_name.biz (use the name of the firmware you want to upload)
Then be patient and do not disrupt the upload. Eventually it will finish. Then set it up so that the router boots from it:
Bootstrap# boot system flash file_name.biz
Hopefully the router will reboot fine with the new firmware. In case the configuration file is also corrupt, you can press the reset button before you replace the firmware and check if it will boot normally with default settings.
If neither the firmware, nor the configuration caused this problem, something could be wrong with your boot code or hardware - contact Adtran for advice/replacement/repair.
Hope this helps.