Why won't ps3 update via internet or storage media?

i tried updating my ps3 through internet several times and everytime i do, it gets over 50% downloaded then says theres either an error, the fie may be corrupted, or the download could not be completed. then i tried it through storage media with thre different flash drives, 2 different computers, and followed all the istructoins from playstation.com very carefully but everytime i'd do this it goes past 50% and says the file is corrupted. I've also updaed my ps3 through storae media before and had no problems.