Problems loading onto new hard drive

[Expatriate]

I've spent the past year running Kubuntu off of an external hard drive connected to USB port. It allows me to load Kubuntu/run Linux programs from any computer (home or office). Recently the external hard drive has shown signs of failing (freezing and clicking noises), so I purchased a Western Digital 2TB Passport drive as a replacement. I tried loading Kubuntu from an .iso disk, same as before, and everything seemed to work fine. When I tried booting from external drive, however, I get "error: no such device..." and then "grub rescue" (or something like this, going from memory). Loading Windows from installed/internal HD still works fine, didn't mess that up (thank goodness), but can't get Kubuntu to load from external HD. I've loaded/run Ubuntu/Kubuntu off of various hard/flash drives for a while now, and have never encountered this message before, so not sure what went wrong this time around. I'm also painfully limited with tech experiences, so any help will need to involve a lot of hand holding and detailed explanation. Thanks in advance, Expatriate

[Snowhog]

It may be that Grub was installed to the internal HD, and has an entry for the external USB HD. If you have more than one USB port, connect the original external HD and the new one and reboot.