C-500 digitizer issue

[Lokifish]

I recently purchased a C-500 from ebay and am having some issues. From time to time the digitizer stops working. Sometimes a reboot works, sometimes removing the battery/holding down power and reset works. Then there are times just leaving it alone for a couple hours works or removing and reinstalling the ram works. Has anybody had the same issues? If so, what was the cause/fix?

[ReflexNPG]

I have the same problem on 2 of my 3 C-500.

Please, if someone knows anything about how to fix or prevent this, tell us!