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.
I've attempted a number of actions, all of which have failed to resolve the problem. I still have circuitmaker installed, and am able to rotate components there. I have uninstalled and reinstalled circuitstudio. I have removed settings from the data folder in public documents, appdata, and the registry. The only explanation that I can think of is that a windows update has somehow disabled this feature. I am using the trial version but was fully intending to buy the product after trying it out. However, because this is such a fundamental feature, I will not buy the product until this issue is resolved. I hear that a new Circuitmaker Pro is coming out; perhaps that will resolve the issue.
When I first installed CircuitStudio, I was able to rotate components with the spacebar. For some reason, I can no longer do this. Pressing the spacebar does nothing, but if I using Move > Rotate Selection, I can rotate the component. Using the latter method is, however, intolerable for rotating multiple components during the layout process. I have tried reinstalling the product, but to no avail. Has anyone else had this problem?