Hi. First do not record anything more on that memory stick and do not format it.
Do you still have goot photo you miss on that memory stick?
Can you still see them on the camera or is that only a problem on the computer side?
What do you use ont he computer, a memory card reader or the computer slot directly?
Can you tell me what is the type of memory stick (what is wrote on it)?
Look like the card corrupted physically. hopefully only the file system did.Here is a software that can scan the card and extract data to reconstruct corrupted data (fully but in some case partially). It is a very long process because it often read blocks many time and do an average.http://www.artplus.hr/adapps/eng/dpr.htmOnce you get enough picture back, if only the file system was corrupted, you may be able to re-use it after a format in the camera.
Do you mean it froze as being non responsive or seemed to take too much time. Because that kind of scaning app take hours to scan cards, i usually start them before going to bed and sometime they have not yet finished in the morning.
Perhaps you can test it on someone else PC with better luck. You may also try to disable any OS update capability when you are doing this, like unplugin the internet. Make sure you also have a good amount of free ram and free disk space.
The app in demo mode allow you to see how much data it can recover, you just can't save it. Sadly there is not much good program that allo to scan unmontable volume.