I don't think the update caused the problem actually. Did you try to just restart your PC?
Anyways, if it still doesn't work, just in case, you could go to your installation folder, open the osu!.cfg archive, and change the line _ReleaseStream to Stable, instead of Stable40, save the archive and run osu!, though I don't think it will change anything, if it's being stuck in the initialization.