Be wary of resetting your password, as that is known to lock you out of your account for 4-5 days and nothing that calling can do to help.

You may have to clear Marriott related cookies... I've seen various issues where whatever cookie they saved end up not working when they update the lipstick on the website. Deleting them lets things function slightly better for a bit, but obvious won't fix their back end IT dumpster fire.