I am new to linux, and probably i did something stupid and now i am in big trouble.
So what happened is i have two os: linux and windows. I needed to unplug one of my old harddrives and plug in my friends hard drive to burn his data on cd. His hardrive was a FAT32. Mine, the one i unplugged was NTFS. So, first i wanted to burn data from it in linux and i rebooted in linux... and figured out this new hard drive needs to be mounted so i changed my mind and rebooted in windows. Windows detected the new hard drive i did whatever i needed t o do, i unplug my friend's hard drive, put mine back in, and then i rebooted back in linux to continue my work - here's where i realised that i am in big trouble. I tried to mount my old NTFS hard drive... it works but for some reason it shows file structure of my friend's FAT32 hard drive. So i thought maybe it's a glitch, i rebooted in windows again... same thing! At last, i unplugged this hard drive and tried on totally different computer with Windows, and the same problem my NTFS hard drive but file structure on it is wrong. Obviously none of these files and directories cannot be read, it's all corrupted. Where did my old NTFS filestructure go? How can I recover it? Is it possible. Please help me what to do, either in linux or windows, i dont care no more, i just want my old file structure working back.

So, fdisk -l gives me this:

Disk /dev/hdb: 40.0 GB, 40027029504 bytes
255 heads, 63 sectors/track, 4866 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/hdb1 * 1 4865 39078081 7 HPFS/NTFS

While "dmesg | tail" gives this:
FAT: Filesystem panic (dev hdb1)
invalid access to FAT (entry 0x001f01ff)
FAT: Filesystem panic (dev hdb1)
invalid access to FAT (entry 0x001f01ff)
FAT: Filesystem panic (dev hdb1)
invalid access to FAT (entry 0x001f01ff)
FAT: Filesystem panic (dev hdb1)
invalid access to FAT (entry 0x001f01ff)
FAT: bogus number of FAT structure
VFS: Can't find a valid FAT filesystem on dev hdb.

Thanks!

Did you shut down the system before removing the fat disk and installing the ntfs disk? I think maybe that is where you messed up, but I don't know what to do about it now. Maybe run chkdsk (or scandisk for older windows versions) on the volume.

yes, i shut down the computer and turned it off before unplug and replugging... i dont know how is this possible, maybe some virus or glitch. I doubt it's a virus though, because i have antivirus software running on my main hard drive. chkdsk scandisk dont help, it gives plenty of errors obviously. I downloaded one software which is supposed to help to restore partition table, but i decided not to use yet. Now i am running for 30 hrs already recovery software on that hard drive. The only option that works to restore my files in my case using this recovery software is the one where i can recover my files but not their filenames. i estimate it will take 40-50 hrs in total. When I recover my files, i will try to run that partition table restoration software, but i am not sure it will help, i might just format my hard drive.

My question now is whether I can actually delete a partition table without traces (the faulty FAT partition) without doing low level format. Maybe then my Recovery software could detect that there was NTFS partition at some point then i could obviously recover more files from it than now and much quicker.