Hey... isn't this the second time this year you're pestering about this year? How many times do I have to tell you that you have to assign it a drive letter?!? 😀
If you have data on it, then as @BigBadBeef mentioned you should assign a different drive letter to the external. And here's another tutorial that can shed some light on how to do that: http://products.wdc.com/support/kb.ashx?id=aLqCzk