Thanks Jim, problem solved rotfl!
If it might be of any help for others, here is what I did.
umount /dev/sda3 –> I got me a message saying that it wasn’t mounted.
xfs_repair –> I got a list of options to use.
xfs_repair -v /dev/sda3 –> the -v option = verbose output from scan. The output said that if I couldn’t mount the filesystem, I should delete the metadata in the log file.
xfs_repair -L /dev/sda3 –> I deleted the log file by using the -L option.
xfs_repair /dev/sda3 –> repaired the metadata.
After that I rebooted.