We’d be happy to help you. Having the right driver and having it work is usually a matter of following a few basic checklist steps..

The Driver, for example, is not the “Yamaha driver” - we need to be specific about the name, the version, and the computer type. Yamaha makes many different keyboards, some use different drivers - so we need to be specific about the name and version number and computer type and operating system.
You have provided none of this information.

The driver you want is the “Yamaha Steinberg USB Driver” version 2.0.3 for Windows (if you have a Windows PC), or version 2.0.3 for Macintosh (if your computer is a Mac)

Let’s start by confirming the Driver by name and version. And the computer type, and operating system so we can help you troubleshoot your system.

You say it worked previously, and now it no longer works. This is good — it means you are or have been setup properly.
Can you elaborate on how you know it is no longer working. By this we mean, if you received an error message from your computer saying it is no longer working, please quote that error message exactly. Computers only have but so many error messages and it retrieves the appropriate error message to match the issue.
If you simply cannot get it work, (no error messages) that is very different from your computer reporting “this driver is no working”...

Let us know, right now we have nothing specific to work with...

Generally speaking...
In the MONTAGE, press [UTILITY] > “Settings” > “MIDI I/O” > set the MIDI I/O = USB (green)
When you have a working USB connection between the MONTAGE and your computer, the USB logo appears in bright blue on the very top line of the MONTAGE screen.

Be sure to have the MONTAGE connected and powered On, when you launch Cubase. During the Cubase launch, you can see it scanning what resources are available, it is during this that it will find and establish connection with the MONTAGE. It will restore the most recent connections.

In Cubase, go to STUDIO > STUDIO SETUP... > VST AUDIO SYSTEM > here you need to select “MONTAGE” or “Yamaha Steinberg USB” as your “ASIO Device”. If you are using a Mac the option will be “MONTAGE”, if you’re using a Windows computer your selection will be “Yamaha Steinberg USB”