Just make sure you're regularly backing up your hard drive - if you have another one at home (external), then that should help or you can always use a backup service like mozy.
There might hundreds of thousands of pixels which can fit on a screen these days but if one dies that it can still prove to be frustratingly distracting. Fortunately, some clever LCD software has managed to fix this annoying problem.
They can get stolen or hacked.
It may die, crash, get a virus, get hacked or stolen. Endless answer really, but nothing may happen to it :)
Like downloading a virus into your computer and there goes everything.