On some of the switches the boot menu will have a password recovery procedure. This should get you a one time access to the switch, you can then copy configs and change user credentials. worth looking into, hope it helps. 
I have 1 PowerConnect 5212, & 2 5324 switches that the previous admin left no configuration information for (at least they had the IP labeled on the front). Tried reaching out to previous admin, no luck as of yet. That said, without doing a complete reset to factory defaults (thus wiping out any possible non-default configuration on these switches) can I do with these? I am pretty sure they have some vlan/etc configuration otherwise I would just wipe them. What are the default credentials for these switches & any way I can get perhaps even the userid in use on these so I can wildly try random passwords? Thanks! 
Trying to gain access to 3 Dell switches - 1 5212 & 2 5324