Hi ILSpam,
FCOM 4.6.20. MCDU Locked or blank procedure may help.
If it doesn't recover, then you'll be stuck with what you have displayed.
If you can't get what you want, then manual tuning of radio aids, manual speed selections, use of Heading and Open Descent etc, and you will still be better off than we were in the old days.
The autopilot will still lock onto an ILS, but you may not be able to do a fully managed NPA unless you'd entered it before the MCDU problem and the flight plan sequences automatically for you - if not - then selected / selected.