On some computers, Kage exhibits rather strange symptoms, not only being very slow itself, but also slowing down the entire system. I am sorry, but I couldn't find a way to fix that bug yet. Try the following:
Right-click on your desktop, select "Properties".
Click "Settings" tab, then "Advanced" button.
Click "Troubleshoot" tab.
There is a "Hardware acceleration" slider. Yours is likely to be set to "Full". Move it one notch to the left, click "Apply" button, then "OK" and "OK" again. The problem should disappear. This operation will not affect performance of your system. Well, probably.