device manager not working

When you say blank what do you mean?  Do you at least see the computer's name in it?

 

If you click view under device manager, what options is selected?  Devices by type is default.

 

Under view>customize, make sure everything is checked except for Console tree, Description bar, and Action bar (unless you want them checked off).

Are you signed in with an Administrator acct? Standard Users might not have access to Device Mgr.