Replying to Recovering data off of a hard drive

In April I bought a 1.5 TB Seagate External hard drive to use only as a backup, I was running OSX at the time. A month ago I bought a PC. I backed up my backup drive and reformatted it to the NTFS format. I then put files back on it. I accessed some of the files too so I know the copy was successful. About a week ago I reformatted my computer and now when I try and access my hard drive I get a prompt saying either there is no partition on the disc or the disc is empty. I took it to a computer store (reliable, done work for me in the past) and he couldnt access it either. I contacted Seagate and they want anywhere from $350-$3500 to recover my data. Some of the stuff on there was irreplaceable but none of it is worth that kind of cash. Anyone have any suggestions?

BTW my current operating system is 64 bit Vista