Hi Code Monkey,
Could you contact EPi Support? Placing the license file in the root of Commerce Manager should do it. Could be that your license isn't valid.
In addition to Tobias's answer, is your front-end site working? Note that your front-end site and Commerce manager site are separated sites and need to put the license in root folders of both two sites.
Can anyone tell me how can I install the license correctly? I requested the commerce developer license for our dev environment - EPiServerCommerceLicense.config and drop into the commerce manager root folder, but i still received the following exceiption
Product/Installation Support Information
Exception: Failed to check the license.