If you can't read it on two PCs, the chances are it would need forensic data recovery, which is massively expensive. Run a CHKDSK and see if that can do anything but, tbh, if it can't I feel you have lost your data.
It's a bit late to say this, but for the future, never rely on a single backup of critical data, particularly if it's on a hard drive. I have a daily routine to copy all critical data to an internal HD, plus two external HDs and a DVD-RW (one for each day of the week). In addition, on Wednesdays I backup to another external HD which I keep off site, and do the same with a second external HD on Saturdays, again kept off site but at a different location. I'm a wee bit paranoid about backups, but since I used to earn my living from computer files, I learnt quickly that the investment in backups was worth every penny.