I've touched on this before but this time around my problem has been much more severe. The BlackBerry would white screen almost daily, sometimes more often than that, and I wouldn't be able to reuse the phone until I had taken out the battery and rebooted while plugged into power. This hinted at a battery problem but I wasn't entirely sure so I first tried to reinstall the OS to see if that fixed it. It didn't. After some more troubleshooting etc. I've since replaced the battery and that seems to have solved the problem.
Interestingly, when I removed the old battery I noticed it was slightly swollen in the centre which I had always thought was normal, but it actually turns out this is the sign of an overcharged battery. Although most of the sites I've referred to say it's not dangerous, they all agree it can't be fixed.
A simple rule of thumb (pardon the pun) is if you can spin your battery on a flat surface and it spins for quite a while, it's got a bit of a swell which means damaged cells. If you spin the battery for about half a rotation before the friction slows it down then the battery is pretty much flat (physically, not chemically) and that's fine.
So if you're having white screen problems on your BB similar to mine, try checking out your battery.
Go on, give it a spin!