Is it possible to recover lost data from a hard disk?

I was using a hard disk, and needed to partition it. I also had a spare second hard disk (Model: Maxtor 2B020H1) which I hadnt been using for some years. So I thought I would use this spare hard disk to back up my data from the hard disk i needed to partition. I copied all the data (about 13 GB, mostly pictures) from first to the second hard disk. When I had finished partitioning, I connected the the spare MAXTOR hard disk again to copy back the data, but I was SHOCKED to see that it wasnt opening. I had saved the data on D drive, but now when I try to open it, a message shows up saying that I need to format it because it hasnt been formatted yet. And when I point the mouse on it, it also shows that the size of the data on it is 0 bytes!!! I am afraid that if I do format it, I will lose any chance of recovering the data. May be its also relevant to tell that I ran Windows CHKDSK on it i.e the D drive when I restarted the PC. Pls help. The data was very important.