We don't really have enough details to go on here. We don't even know what type of partition it was or if you know what type of partition it was.

The BIOS sees the drive. That has very little to do with the partitions on the drive. You should have these two concepts very clear in your mind before you go any further. You best bet of action here is to uderstand a lot before you make any change that may get you data base. The wrong move may make things far worse.

If you have any insight on what happened to the partition, it would be wise to share it.

There is a program in Knoppix called gpart that can try to recover a partition table for you. If your partition table is what is messed up then maybe this will allow you to recover it and get the files back. But undertsand that if the data in the partition itself is corrupt rather than the partition table, this will not help you recover it. I would suggest reading up on gpart, but I wouldn't actually run it until I better understood the true nature of the problem.

There are also file recovery tools that try to recover files from corrupt windows partitions. I have not had good luck with them and can't make useful recomendataions.

You may also want to look at the Live Linux CD called Helix.