Iomega 640GB hard drive not recognised. I have recently purchaced an iomega 640GB ex hard drive

Question

I have recently purchaced an iomega 640GB ex hard drive for my Sony Vaio VGX entertainment pc. I have loaded the disc and when i first used it it appeared ok, then after i shut the pc down and turned the hard drive off then restarted it all the following day it no longer recognises the drive and the hard drive is making a constant ticking noise. Whasssup?