It's been a few years, but I will try. It's a bit of a memory dump I'm afraid
- Do you have serial console access to the Service Processor of the chassis? You would need a serial connection in at 19200 BAUD (not the default 9600 for most clients) and this may allow you in somewhere to a set of text based menus to get this set. Credentials might be admin and admin. I needed to get an appropriate crossover cable. I bought one via a generic online auction site for about 2GBP but it's too long ago to get the item information.
- Can you HTTP to the service processor (physical port labelled as HMCn, default address 192.168.0.1 I think) You can get a GUI interface to the similar thing.
You would need to define the HMC account password in there. When you use your HMC to connect, it will generate SSH keys to keep the connection, even if you change the password later on.
I hope this helps, but sadly it is likely to be incomplete.
Robin