This will happen with newer versions of windows server because Microsoft has disabled interactive services in windows by default.
When you load 3DM2 web, you will likely see the following error in your event viewer log.
The 3ware 3DM2 service is marked as an interactive service. However, the system is configured to not allow interactive services. This service may not function properly.
To solve this, you can enable interactive services by making a registry update.
You need to update the DWORD registry entry for NoInteractiveServices from 1 to 0
Once you've done this restart your server and 3ware 3DM2 web interface should once again show the controller(s).