The first thing to do is power on holding down the option key. If you get the option menu, you know it's not a video chip or video hardware issue, and your computer is likely fine aside from whatever is going on with the hard drive. There's no reason to mess with the hardware until you've tried this. It's also possible the HD is fine, but just needs an OS reinstall. It is odd that you don't mention eventually getting a flashing folder icon...the lack of this tends to point in the direction of video hardware. But again, start with the option key. A PRAM issue is unlikely.
These PowerBooks also have chronic issues with bad RAM slots, and they are also touchy as far as what RAM they will take, especially if you have two modules that aren't identical. A white screen is not a typical symptom of a bad slot, but in order to be thorough and to rule it out, you should power on with one slot empty, and then with the other slot empty.