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Can you turn the FP-4 Off? if so, then you can Reset the unit using button pushes, which might clear up the problem. But you may be unable to do so.
Instead, try unplugging the unit, for 4 hours. (And disconnect it from everything else, and remove any add-ons.) Then plug in again, turn On, see if the problem is cleared up.
After that, a Factory Reset power-up, in which you turn the device On while holding down the Function button for at least until 'Fct' appears on the display, will clear all custom setting out of the device, but might restore functioning.
Note: do not turn the device Off during the Factory Reset.
(I regret that I am not able to offer Live Phone Call service at this time; However, your request is still open to other Experts in this category, and one of them may pick up on it at any time.)
If you followed my instructions in every detail, and still got no response/change/improvement, that (I think) settles it: your device is 'broken' enough to need service-repairing.
What is your local zip code? if you are interested in at least getting an estimate on the price of repair-servicing, I will give you contact information for Roland Authorized service locations in your region.