External Hard Drive-How can I tell if it is really dead?

Here is the situation. I have a WD Mybook Premium II 1 TB External Hard drive. Recently it stopped working-I was not able to access any of the data on the drive. I did not make any recent changes to my hardware. I use Vista/

I tried to reformat it via Disk Management and clicking on the icon under "My Computer"
It will not allow me to do it. I get a windows error message saying "Windows Could Not Complete The Format" . I can get the drive to show up under "My computer" but the drive is blank..and as I said previously, I cannot access any data or reformat it.

I am not sure what else I can do to find out if the drive is really dead or not. I am assuming that it is, but I want to be sure before I go spring for another drive.

Download the hdd diag program from WD and create a boot disk with it and let it look at the hdd..If the hdd is good you will get a 000 error code then,,,
You might have to do a quick erase and re fdisk the hdd,I find it best to do my fdisking from a DOS boot disk as I have had repeated problems doing so from windoze and when it snafu's ,as it surely will,it cannot be fixed if the original formatting etc was done from windoze..