It may be possible that your rotation step got changed to 0 or 360. Try this:
Go to your Preferences and under PCB Editor, look to see what your Rotation Step is set to. I have mine set to 45.000. You might have a different number. If you choose to change it, make sure that it is in multiples of 90 degrees, such as 10, 15, 30, 45, 90.
There is a possibility that you've somehow disabled the feature. I am uncertain how to disable or enable quick keys.
When you reinstall CircuitStudio, all of your settings should be retained in a folder somewhere unless you delete them when you uninstall CS.