You most likely enabled Compatibility mode.
Hold shift while starting osu! until a recovery window pops up. From there you can disable compatibility mode and start osu!.
If that recovery dialog does not start, navigate to your osu! folder and edit the file "osu!.pcname.cfg" in notepad. Find the line CompatibilityContext and set it to 0. Save the file and start osu! normally.
These are only temporary solutions, as soon as you enable compatibility mode again, the error will reappear. For a permanent solution, update your Intel graphics drivers past version 15.46, as Intel released a fix for this specific issue in their newer drivers.