Try to run your osu! in Windows 7/8/8.1 Compatibility Mode and see if it works
If you don't know,
1. Go to osu! directory
2. Right click osu.exe
3. Click Properties
4. Go to Compatibility Tab
5. Click "Run this program in compatibility mode for:
6. Select one of the options above and click OK
If you don't know,
1. Go to osu! directory
2. Right click osu.exe
3. Click Properties
4. Go to Compatibility Tab
5. Click "Run this program in compatibility mode for:
6. Select one of the options above and click OK