Screen Text Dissapearing

Just bought a used 500 and i've been having this problem, while trying to use certain functions, like loading samples or in the record mode. After a short while the text will disappear and then it seems the buttons will be non-responsive, so I have to power down and up again. This has happened more then 5 times in the last ten minutes. Any ideas?

Actually the buttons seem responsive, its just the text that disapears, while the back light remains lit.

hmmm, could it be the ram. Okay I had a third party ram upgrade installed, I took it out, and now the problem is fixed.

Oh man, you answered before I replied. I was gonna say that its a glitch in the system and not the screen. Glad you pinpointed it.