Disappearing curser

I have a 17" powerbook G4 running 10.4.11 The curser just disappears while I am typing and everything becomes frozen. The only remedy is to hold the power button down until it shuts down, causing loss of anything that had not been saved up to that point. I have bought a new battery and have also reset the system management controller, PRAM, and the NVRAM. But this has not solved the problem, it is just less frequent. I do a lot of word processing on this computer and it is useless to me if this continues. Is there a solution to this problem?