If you have opened the drive, only expensive data recovery services can help you now. Hard drives are not meant to be opened outside a cleanroom.
Casey
Opening a hard drive doesn't mean it will be unreadable every time. I've opened and closed dozens of harddrives and still be able to read data off of them. I've even transplanted platters from a dead drive to another and been able to recover data this way.
@OP: As my previous post mentions, back up the data if you can. If you can't you are likely out of luck.