I accidentally converted my 1TB external drive from NTFS to EXT3. I have a ton of data on the drive and I believe the data should still be there. Is there any way to either convert it back to NTFS without loosing the data or recover the data in its current state (EXT3)?
Testdisk will attempt to find and repair your NTFS partition. It's command line based and can be quite daunting to use. Second PC open on the website helps. At some stage this software makes changes to your disk so you may want to try one of the non-destructive file recovery utilities first. I recovered an NTFS partition after an NTFS format using this.
I've had luck in the past using magicrescue. It scans your harddrive and recovers all files matching an extension you specify.
This would scan the sda6 hard drive partition for deleted jpeg and png files and output them to the outputfolder:
Be sure you have enough space on the target partition to write the data to. This will try to recover any deleted files that it finds, and you can easily end up with gigabytes of data written to the target. Also, make sure your target folder is on a different partition (or drive) than the drive you are scanning.
If you formatted your entire drive, you will need a second drive to accomplish this, either an external drive or a second internal drive.
magicrescue also recommends that you don't do anything with the drive between now and when you start to run magicrescue. Booting, saving or retrieving files, and other operations can make your files unrecoverable. Running magicrescue sooner than later will help you get the bet results.