Hi, thanks for your reply sberlin

To answer your questions, yes I was using succesfully Limewire 4.2.6 before that happened, just before in the day it was working good. But Here there's something I forgot to mention that might be important: so Limewire was running, but suddendly I ran out of memory space, so I had a message like "Limewire can't save downloads anymore, no more space found on the computer(...)". I clicked ok on this message, wich was repeated 4 times. Then I shut down Limewire. Then I made some space on my hard drive (a few gigas), then I launched Limewire again, and then it reinstalled itself like I was saying in previous message.
Seeing it was not recognizing past downloads, I changed the settings to have the same 'Save Directory' as I had before, I shut down and restart Limewire but the same problem was remaining.

If I understand what you say about .dat files, it's too late to do something with that : I stopped & restart Limewire a few times since it was working ok, so I guess .dat files have already been overwriten.

Thanks again for helpin'