MacBook pro not recognizing external HD used for time machine on an old mac

Hi

One question. Bought a new Macbook pro and copied the files from my previous mac using the FireWire. After some days I wanted to format my external hard drive which I've used on my old mac for time machine. The problem is that my new mac is not recognizing my external HD. There is not even the HD icon appearing on the desktop.

Can anyone tell me why this might be happening? I've tried the HD on a PC just to see if it works and it does. Is just the MacBook which is not recognizing it.

thanks

So you are saying it's not even showing up in Disk Utilities? Since you have another Mac you can always try formatting in your second Mac and then try to connect it again to your first Mac. If it still doesn't show up then there is some other problem going on.

Are all the cables secure? I had this happen to me a while ago, and it turned out the only problem was that the usb cable plugged into the external drive wasn't seated all the way in.

Now, if all the cables are seated property and you can see that the external drive is working (the light on it is on or whatever), and it still doesn't show up even in Disk Utility then you have a really big problem.