oh screw the retard comments... I unplug and plug things just for the heck of it... just three days ago, I was hotswapping one of my SATA and blew one (SATA can be hotswapped) ... big deal! Don't be so scared to touch your components. (long time ago, when I was a kid, I was wearing rubber soles and rubber gloves, while checking to see if the IDE was firmly in place... now I rub my hands on my silk shirt, then I push it down with my thumb, while rubbing my wool socks on the carpet.... welcome to the world of RMAs....)
anyhow.. from my countless experiences with harddrive failures, since I own like 18... from my precious 2gb IBM (now a collector's item) to 250gb SATAs..
I think there are three possiblities here.
1. Your physical disk is screwed up aka the mechancial parts that make up your disk (in this case, you can't really fix anything or recover any. Although in the past, I voided my warranty, but actually cracked opened my problematic HD and replaced some parts with the same model components... and it worked! and I got my files back.. but I don't recommend this.. unless you know what you are doing) When your physical disk is screwed. Some mobos will not recognize, but some will. I found that SCSI controllers via PCI can sometimes recognize the drive better than mobos.. so try it, if you have one of those cards.
2. Your controller card is burned out or screwed (this is fairly easy to fix. all you need is an identical harddrive... replace the controller cards and boot, and voila! there are your files again. Back it up. Remember to put the controller card back to its original owner and RMA the whacked one.
3. Jumper/Cable/Mobo/Any Other problems not listed.... This is easy to test. Just take the HD to another computer, set it to master in secondary IDE and plug it in (after taking the secondary IDE part first of course)... If it doesn't work then your problem is either 1 or 2.
BTW, if you decide to go with route 1, because those files are so sensitive... there is nothing like recoverying your precious data from supposedly dead and fried HD... wow! it's feels really really good.