My ibook g4 will boot up to the desktop page and even run for about 30 seconds. It loads os 10. Not leopard, the one before that. After about 30 seconds it goes to sleep. When I wake it up the screen doesn't become bright enough to see...You can see it but just barely and then it only stays awake for about 10 seconds. Then it goes back to sleep...What can I do to fix it?