Xbox 360 120GB Hard Drive

For Original Xbox games to be playable on an Xbox 360, it needs to be an official Microsoft Hard Drive.

However, there is no official 120GB hard drive for the Slim, only 250GB and 320GB.

There is a 120GB for the original-style Xbox 360 and the later Elite, but not Slim.

If you are using a Slim, the hard drive itself will be the problem and you will need an official one.

The hard drives for the Xbox 360 slim are pretty cheap anyways. Here are some fairly cheap ones:

120GB:
www.rakuten.com/.../224172078.html

250GB:
www.ecrater.com/.../internal-250gb-hard-drive-for-xbox-360

To play Original Xbox games, you need an official Microsoft hard drive.

There is no official 120GB hard drive for the Slim. For the Slim, the hard drives are 250GB and 320GB (and one with 4GB internal flash memory); there is a 120GB hard drive for the first iteration Xbox 360 and later Elite console.

So if you're sure yours is the Slim variant, the hard drive itself will be the problem.

No just a regular Xbox 360 with a 4GB hard drive. I purchased and added the 120GB.

When you transferred the content over to the new hard drive, did you have the old or new hard drive plugged into the transfer cable?

If you had the 120GB hard drive plugged into the transfer cable that may be where the issue is being caused, would you be able to transfer the data back to the 20GB hard drive, plug the 120GB hard drive into your console, format it then try transferring
the data back to the 120GB hard drive with the 20GB hard drive plugged into the transfer cable and the 120GB hard drive plugged into the console.

Scroll down and follow the "Format a storage device":
support.xbox.com/.../storage

Let us know how it goes!