Some controllers may require the latest available drivers in order to be compatible with Serato DJ.
It is important to make sure all your drivers and firmware are up-to-date from your hardware manufacturer before running Serato software. If you have purchased a new controller, check for any updates before using the device as you may run into issues if you are running an older, incompatible or outdated driver.
You can find information on where to find your drivers here.
Be sure to select your hardware manufacturer to be redirected to their website, then find your product, and check any updates they may have.