when it happened to me, I cried. a lot.
about 18 months ago that happened to me, well except my EHD didn't get knocked down, it just suddenly freaked out. I took it to Best Buy's geek squad and they couldn't fix it so they sent it to a data recovery place. The discs in the EHD had misaligned and they had to rebuild the EHD in a 'clean room'. It cost me about $1800
It was so much money that I almost didn't do it but my hubby was insistent because when he was a child a fire destroyed all his childhood pics. He didn't want that to happen to our kids. Now I have everything on DVD, on another EHD, and backed up to Mozy.
I'm so so so sorry. ((hugs)) Hope yours is an easier and cheaper fix.