ive tried using putty, dcc and filezilla, all coming up with incorrect password, even though on dcc it briefly connects to telnet for a couple of seconds
Someone must have changed the password at some point so either you have changed it/the person you bought the box from has changed it or your using some corrupt backup image where the password has been reset to something other than default passwords.
You have a few options.
1: search for a root password changer plugin for blackhole either via your addon server or google/there is 2 types of plugins/1 requires the old password which is of no use to you so you need the plugin that changes the root password and shows it to you on your tv screen which you copy down/i know its available for certain images but i,m not sure about bh images.
2: factory reset/this will wipe all configs so be warned.
3: reflash your box with a clean image or maybe even a backup from this site if you prefer.
MK