I was getting messages that my drive was full so I opened Dolphin and started deleting files. Even after emptying the trash, Dolphin still reported that the drive was full. I rebooted the computer. Now I can't log in. When I type my password, the system just freezes. Tried multiple times. Same result.
This isn't an actionable bug report, I'm afraid. It's too vague, and there is no debugging information. I suggest you first ry a support forum (e.g. forum.kde.org, reddit.com/r/linuxquestions) and ask for some help resolving the issue. Once it's resolved, you and others can figure out what exactly the software bug is, if any, and then file a new, more targeted bug report.