I did much photoshopping on pictures, of which I can't remember the original. The originals are gone. Can I retrieve them still?
The odds are against it, if you didn't take care of your files then you really only have yourself to blame.
That said, there is a feature called "previous versions" in Windows which has been around for quite some time and, if enabled, may save your bacon provided system restore was/is configured correctly, which it may have been by default.
Probably not, unless you saved in Photoshop's native format and the files have a layer which corresponds to the original unaltered image. If you saved in jpeg or another "flat" format — or if you edited the image directly without using layers — you are going to be out of luck.
It is impossible to get original images back in Photoshop. File recovery software are available. There is no way if you overwrite the edited one with the originals..