Check Archived Log Destination
At this moment, you should make sure the destinations of archived logs and data files are in the same directory with software or not. If they are all together, you should check the archived log destination first. If necessary, release the space of archived log destination as quickly as possible.
All Logs Stop Writing
Mostly, the archived log destination and data files are separate mount points from the software. In such case, the database seems to service to public, but it's much slower than normal. This is because diagnostic logs (alert log and trace files) and networking logs (listener and sqlnet log) are unable to write logs. There'll be no further error message that you can trace if your database suffers from other problems.
Hint: Everything is Slow
How do we know the database problem is caused by 100% full of software directory before checking it? Does there any hint can imply this? Slow on everything is the only hint we can have. Of course, clearing obsolete logs is the only thing you can do.