While I've worked on a lot of older boxes I can't guess what the settings are. The person who setup this Sonicwall may have set it to non-default baud so try 9600 to 115000.
Also ask Sonicwall for a manual and a new cable.
I have a Sonicwall 3500, I tried using a Cisco console cable and change the settings on Putty to the following:
BUAD:115200
Data bits:8
Stop bits:1
Parity: None
Flow Control: off
This is what a couple other forums suggested, but still can't console into it. Does anybody have anymore ideas?

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