Older Intel iMac, 500 GB WD drive dedicated to Time Machine. The Cylon eye is moving back and forth, I switched around cables but just have a blank spot where it is supposed to show up. Not found anywhere on the computer. Is it time for a trip to Best Buy. Can any hard drive for Mac be used for Time Machine. The defective one is more than a few years old. I'm looking to do this on the cheap.