Well that sucks. You may have already looked at this but the xbox support site says:
Solutions
Find solutions to common Xbox 360 Hard Drive problems.
The console does not detect the hard drive
If your Xbox 360 console does not detect an attached hard drive, try the following:
Turn your console off and then on again.
Make sure your hard drive is installed correctly by removing and adding your hard drive back again.
If you have another hard drive, try it with your console.
Replace your hard drive. You can order a replacement Xbox 360 Hard Drive from the Xbox Online Service Center. Console registration is required to replace a hard drive under warranty (the hard drive warranty is the same as your console warranty).
If the above steps don?t resolve the problem, repair your console (sign in with your Windows Live ID, if prompted).
"No space available" error
Try the following:
Free space on the storage device.
Use another storage device.
"The destination device is full" error
Try the following:
Free space on the storage device.
Use another storage device.
"Can?t transfer item" error
Try the following:
Turn your console off and then on again.
Not all items are transferable. If you receive this message, you can't transfer the item.
Link: http://support.xbox.com/en-US/xbox-360/settings-and-initial-setup/hard-drive
