Blackberry 8310 Blank Screen

Question

Hi. My blackberry screen often (4-8) times a day just goes white for no reason. Nothign can be seen on the screen. The phone still works, but without the screen, it is obviously difficult to navigate etc... Sometimes, it will just sort itself out and come back, but other times I will need to repeatedly take the battery off and to re-start it. Doesn't always work though. It's summer here, so I thought the phone was over heating, but it also happened when it was a cold day.

Any assistance would be appreciated.

Thanks

Marcus