I wanted to save a program (maybe 12 lines of code) and it took a lot of time when I entered SAVE . If I enter CATALOG it just returns a syntax error.
You're using floppies and DOS. Right?
Because this sounds a lot like DOS being detached (*1). That means DOS is no longer active and hooked into command line processing. In that case, a SAVE command would by default save to cassette, which will take some time but other than that issue no further response.
Likewise typing any DOS command - like CATALOG - will lead to a
Syntax ERROR, as BASIC does not know anything about Disks and DOS is not listening.
Detaching DOS may happen if RESET is pressed twice in fast succession.
After a single RESET DOS usually rehooks itself, but if a second RESET comes short enough it will be stopped from doing so.
With old machines this may as well happen due a bouncing reset key.
How to get out?
Of course the most simple way would be classic help desk manner of switching the machine off and on again. Not gentle and not saving any work done.
A bit more gentle might be issuing a PR#6 to reboot without switching off first - still all program and data is lost.
Best would be of course to reconnect DOS (or PRODOS) by doing a
CALL 978 ($3D2) (*2). If that works, all program and data should be still present and the computer work as before. If not Step 1 has to be taken.
*1 - Everything said about DOS works of course the same way for ProDOS.
*2 - Documentation often mentions calling -25153 ($9DBF) instead to reconnects, but that address only works with an unmodified DOS 3.3, so better use the official reconnect call.