Vista - can open external disk

Hi!

I have just put an old internal HD into an external USB box and Vista can't
open it and it is not shown. It appears however in the diskmanager in the
administrator utilities but it is shown as not connected. Can anybody help
me? I have tried to delete the infcache file in the windows/inf folder but it
doesn't allow me to do it neither. How can you do it in vista? I have
administrator rights but I can't do anything :-(. Thank you very much in
advance!

Martin