It sounds from your description as if you're saying you have the SC exploit/installer on the USB memory device but the Xbox doesn't recognise or refuses to work with it. If so, sounds like you have one of the many incompatible USB drives there are.
I assume you:
1). Are using a 4GB memory device or smaller.
2). Did format it to FATX.
3). Did use Xplorer360 to get the the exploit/installer saves onto the device.
If you did all this then you could try another USB drive or, guaranteed to work, Xbox memory card. The latter will require a USB to Xbox controller adapter.
Alternatively read the thread at present literally just below this one, it should set you on the best alternative path.http://forums.xbox-scene.com/index.php?showtopic=743174This post has been edited by fallenangle: Jul 14 2012, 04:00 AM