Depending on the OS, if you right click on My computer and go to properties and the System Protection Tab.
If you see your drive listed twice, one that says on, one that says off.
Go to the properties of the one that says on and completely disable it.
Now there should only be one drive. Re-enable it on that one drive and you should now be good.
I had this recently one 3 Win7 machines and that fixed it for me