I think I just fried my Dad's HD

My mom got a new macbook and i was helping her set it up. My dad has an old model white book and they still have her HD from her old White Book. I switched out the HD's like I've done a million times before and proceeded to boot up her old HD and transfer the files to her new computer.

After an hour or so i finally powered down my dads white book and switched back the harddrives. I forgot to take out the install cd for my mom's new computer.

When my dad booted the computer it gave him the apple and loaded forever, it booted finally from the cd and tried to reinstall. Which of ocurse it cant bc the cd's wont work on other machines.

He is convinced having that cd in there whiped his drive but we all know better. With the cd drive out the computer boots to the ? folder. I don't have his cd's to figure out whats wrong but there is no clicking.. I'm getting his boot cd's tomorrow to try and run disc utility to figure out.. i dont know anything.

I'm afraid it got a shock or something while it was out but I honestly dont know anything about hard drives. I have to figure out how to get his stuff back for him.

Does anyone know
how I can tell what exactly happened to the drive or what is wrong with it? What things shouldn't I try bc they will hurt the data?
What user friendly way there is to recover the data if there is something seriously wrong with the HD?
cost isn't a problem, but I'd like to keep it inexpensive. This is his business HD so we HAVE to recover anything we can.
Any answers would be great. I feel like I just killed his computer for him.

ok so disk utility finds his HD but the start up disk does not. I don't want to repair incase I hurt the files. Does anyone know what I can do from here?

they were identical machines, her old white book and his current whitebook were the exact same computer down to specs and date they were purchased. All I had of her old one was the hard drive so there really wasn't another way. All I did was pull his out and put hers in. It's possible I screwed something up in doing this.

But I just found out his HD wasn't even the original HD for that computer. his computer was smashed by an angry customer who broke into his business and they took his HD and put it in my moms computer.

The HD I was putting back in it to transfer files was the original HD for that computer. With the beating his had taken in the old computer I think me pulling it out was just the final straw....

Oh and he has no backup...

Don't ask me how. I don't know. It's unfathomable to me to have that much important stuff on one computer and no backup. I just have to figure out a way to recover it.