You can manually enter the hdkey to lock the hd again. There should be a file where your eeprom is located called hddinfo.txt containing your hard drive key.
Here is a copy of mine showing the key you need to copy down :-
Disk Serial Number : "WD-WMA9N9004096"
Disk Model Number : "WDC WD80EB-28CGH2 "
HDD Key : cc:67:20:96:e1:bf:17:1f
e4:c9:08:cd:f0:3d:4f:01
82:cf:bc:c0:00:00:00:00
00:00:00:00:00:00:00:00
HDDLockDisablePassword cc 67 20 96 e1 bf 17 1f e4 c9 08 cd f0 3d 4f 01 82 cf bc c0 00 00 00 00 00 00 00 00 00 00 00 00
XboxHDKey c3 81 bd 74 da 4d bf 1d f8 80 7e 01 5b 43 c9 f4
The 40 digit area highlighted will be the hdkey for your system. REMEMBER that it is the first 40 digits, anything after this is irellevant.
Once you have this key boot up with HDM and select option 3 'boot with lock/unlock tools' type 'HDLOCK' at command prompt and enter your key EXACTLY as you wrote it down, double and triple check tht it is correct.
Your drive will now be locked and should work in the Xbox.