If you can, eliminate any security, ACLs, Firewall issues that may be between you and them, and make sure your default-gateway is set on each switch. 
I am trying to run an SNMP scan from my asset management software and it isn't seeing my PowerConnect switches. Most of my switches are 3524's. The scan is using SNMP V1. Is there a setting I am missing to enable the switches to be seen? FYI, I have switch access locked down to HTTPS and SSH if that matters.
Problem With SNMP Scan