Not sure about a quick fix but I sure as h311 had the same problem for a while. Random screen flickering as if the keylock slider were operated. Sometimes it went for all night. Imagine the mess it caused in BackupMenu (for the uninformed, BackupMenu uses the keylock switch as a restart button).

It took me a while to figure out it was caused by moisture. Eventually it fixed itself, I guess just by properly drying out.

Keep it in a dry place (some suggest a bowl of rice (uncooked )) for a couple of days and keep it away from steamy bathrooms and the like.