first Time Machine backup to LaCie stalled

I've used Time Machine forever. This

I just changed external hard drives (for TM) for my iMac backups and am doing my first Time Machine Backup to my new LaCie Rugged 2TB drive.

Everything was going along just fine but now the backup is stalled.

Not only is it stalled, but the computer is unresponsive as well.

No mouse cursor (I disconnected it and reconnected but no go)

No control using keys.

Can't use track pad.

What do I do?

I need my computer responsive again.

Plus, of course, I need to do a TM backup - if not on the new external drive, than on the previous drive I was using (which is perfectly good; it's just too small)

I can call LaCie tomorrow.