I'm assuming you are getting an error message when trying to run the game.
Your GPU does not support the required OpenGL version to run the latest osu! builds. There are two ways to get back to an older version of osu! so that you can play the game:
- Open your osu! folder (the default path is "C:\Users\<Username>\AppData\Local\osu!")
- Edit the file named "osu!.cfg" in notepad (you may need to enable file extensions to make it easier to find)
- Set the "_ReleaseStream" line equal to "Stable" (e.g. _ReleaseStream = Stable)
- Save the file and reopen osu!
If that doesn't work, download
this installer (direct download link) and run it. If you already have a previous osu! installation with maps, skins, etc, make sure you change the installation path to the correct location on your computer. Otherwise it might install to a different location and you will need to move all of your maps and other data over manually.