its not working even if i try this way "rman target username/password@tnsentry"

C:\>rman target testdb1234/krish96@testdb1234

Recovery Manager: Release 10.2.0.3.0 - Production on Mon Oct 8 16:11:06 2012

Copyright (c) 1982, 2005, Oracle. All rights reserved.

C:\>

it still shows c:\> prompt instead connecting to rman ..and also its doesn't display any error's ..

thanks..