today my mac for some reason or another froze. well not froze but acting very sluggish. figured the 4 gig of memory would have solved that.((running only 5 programs mind you)) so i do a hard restart of the computer((pressing and holding the power button)) and when i come back my external is no longer there. hasnt been connected all day! its a western digital 500 gig hard drive. i disconnected everything on it and re instaled it. nothing. i just get the spinning light in the front. bought it in december of 07. any ideas of what could be wrong or what i can do to fix it???