Some keys wont work after my korg pa50sd is turned on

Go To www.korg.com and go to support

For the best info contact Korg customer support. Here is the link-

http://www.korg.com/us/support/contact

There is no adjustment to control the brightness in korg pa50/sd.
It is hardware problem.
-Is the white backlight that is too high?
or
-normal backlight,but words is too dim?

Both of that case,can be caused by damage / change of voltage control for lcd. Perhaps there are parts that are damaged or have changed in value. Typically capacitors etc.
If the backlight is too bright, then the damage is in backlight controller, may transistor or an inverter transformer.
Proceed with the repairs to the experts.

Take it back to where you bought it, and get it serviced, to clean the dirt-filled contacts.

Here is a link to your manual, it should tell you how to do a factory reset somewhere in it. Hope this helps.
http://www.korg.com/uploads/Support/Pa50SD-UM-ENG_634618903911880000.pdf

Please see "Loading Korg Pa50SD's Operating System" below for
instructions on how to load the operating system.

para resetear el pa50sd
Please see "Loading Korg Pa50SD's Operating System" below for
instructions on how to load the operating system.

Have the same issue

NOT a fuse... thaat person knows nothing. There is something wrong for sure. Check if one of the buttons or keys MIGHT be stuck down (depressed). Sometimes the units check that all the control buttons are up and they don't really tell you why they fail to start. Beyond this a repair shop is in order.

1. Power-off the PS60.
2. While holding down the four PERFORMANCE buttons and the OCTAVE DOWN button, power- on the PS60. The PS60 will be initialized, and the factory-set data will be written into internal memory. The display will indicate "Initializing..." while data is being written. Never turn off the power while this indication is shown.

Manual available here:
http://www.korg.co.uk/downloads/ps60/docs/PS60_OM_E1.pdf