Hoping you are such a freak you made loads of backups during your 'expiriment with my bios period' and have one left on your Pc, you can either do this :
use this tut. to format your drive:
http://www.how2xbox.com/harddrive.htmPay attention when booting up with the cd you burned, first step should be to lock your drive using the eeprom you put on the cd, so at start you chooce 3)Linux with locking/unlocking options, and lock your drive
Since error code 5 means: HDD unlocked, i think this is it.
Put the disk back in your box and go....
Option 2 hopes you still have your original xboxdrive lying around (assuming you placed a bigger one in your box, and didnt frie the original one....duh)
Replace the 'unlocked' drive with your original one and it should boot again, from here follow the above mentioned tut. but just use your original drive to ftp the backup you need. Dont screw it up, use it as a backup only!! Saved my ass several times :)
Now unlock your drive and reinstall it in your box, e voila!
Let us know...