Hi.
You don't give me much to go on here, but I guess the first, and most logical thing to check is that you have a seed device and snmp community strings configured for discovery.
Go to:
Campus Manager-->Admin-->Device Discovery
Once on that page, click the "Help" link at the top-right of the page, and context-sensitive help page will open up. If you scroll to the bottom of that page, you should find a couple of links:
"Setting SNMP Credentials"
and
"Specifying Seed Device and IP Address Range
Those are the minimum things you'll have to get through to get discovery going. Check those links out and they should walk you through setting it up with no problems.
Remember, you have to have CDP enabled in your network to discover also...
Good Luck, and HTH,
-J
