I had a similar problem with a Hitachi HDD I had installed - it refused to boot up, coming up with a disk error. Hitachi provided a software widget (Drive Fitness Test) to fix it and recover most of the data, which you can download from their site if you have access to another computer, then run on a 1.44MB disk.
http://www.hitachigst.com/hdd/support/download.htm
Hope this helps.
SBG