I'm trash with computers but I think the best bet is to backup your songs somewhere and completely remove everything osu! from your computer (you can stop here if you want), and then reinstall everything including your backed up songs. I feel like it might be a problem with conflicting osu! files on your computer.
It could also be your hard drive, but if you aren't having problems like this with anything else I'd say it's less likely (but still possible, given how many damn files osu! takes up). Also, you could do a disk cleanup to see if that helps. It takes like 5 seconds to learn how to do.
But yah, definitely backup all your songs from now on so that even if they are corrupted you can reaccess them.
Source: Computer Science and Applications Course I got a B in because I missed assignment due dates lmao