Worse thing that can happen is Solar storm off the sun. Happens every 11 years and this years one is biggest so far on record, there was one long time ago when we first had power, its more or less EMP'ed the hole world so it didn't really effect us back then as we was still in baby stages of technology.
If its happens this time around then we in deep **** say good bye to all your pc's. Say good bye to Japan, all there nuclear power stations will go boom from over heating. But chances of it happening this time around are unknown, last time could of just been bad luck.