Zx don't stay on bed high , can't save annything on printer

hello, i have a problem with ender 5 pro V.1.1.5.
i have searched everything about my problem but found nothing. my Z x does not stay at the bed height, no matter what i do.
bed leveling, firmware flashed. this several times. all done according to Creality movies.
tried with pronterface myself but nothing. what i have noticed is that when i have done my settings and bed leveling and want to save it on the printer that i get no sound for confirmation. also with pronterface i type the code M500 to save, i also get no confirmation that it has been saved.
what could be the problem and how do i solve it.
thanks