How to recover deleted files?

So, I just swapped an internal hard drive from one PC over to another. As soon as I booted up the new machine, it kicked off some kind of automated scan—I think the prompt said "checking file system" or something along those lines. The drive had about 490GB of data on it, but once that scan finished, I looked at the capacity and only 240GB was left. It basically nuked half my files right in front of my eyes. Has anyone dealt with this before? Is there any way to actually recover the data that just vanished into thin air?

Look, it’s totally doable since you’ve got a whole arsenal of data recovery tools at your disposal.
Back in the day, I used to just fire up a bootable rescue CD or a USB drive to get things moving.
Those things were packed with all kinds of software specifically designed to tackle corrupted drives.
Plus, if you don't want to mess with it yourself, there are plenty of pros out there who handle this stuff for a living.

Give the software Reece a shot. I’ve managed to pull quite a bit of lost data back from the brink using that tool. But honestly? If you aren't entirely sure what you're doing, don't play hero—find a pro who actually knows their way around a hard drive.

I guess it’s probably best if you don't try messing with some random software. You should probably just find a local pro in your area; there are definitely guys who actually know what they're doing, you just have to track them down.