The xbox uses a password to unlock the harddisk that is unique for every xbox. It is calculated based upon the xbox hddkey and the harddisk model and serial number. The hddkey is a piece of information stored in the xbox eeprom chip. This is a small (256 bytes) memory chip.
It is possible to lock a harddisk with a pc. There are dos tools and there is the xboxhdm package. This is a linux distro that boots from cd. It has fatx support and buildin scripts to partition and prepare a harddisk for use in a xbox.
So, you should go to your friend and unlock the disk again first.
Then you will need to get your xbox eeprom contents. That eeprom.bin file is needed to calculate the harddisk password for locking.
http://forums.afterd...view.cfm/357863A modchip is also an option. It allows to run programs, even with a blank harddisk in the xbox.
Since you restored the harddisk to factory with slayers, you will need to install the softmod again as well.
So, you will need:
xboxhdm
Kingroach ndure 3.1
An old pc, with 2 ide ports.
If you don't have an old pc, you can try the xboxhdm2 package that ldotsfan created. It boots from an usb stick.
regards.