Lost all data in iTunes and now, when I open the program it appears «iTunes 1» is empty. What shall I do?
You can restore a backup which iTunes creates automatically. Go to My Music > iTunes folder and rename the file iTunes Library.itl to something else like iTunes Library_bad.itl then go to My Music > iTunes > Previous iTunes libraries and select a recent backup. Rename the files to iTunes Library.itl and copy the file in My Music > iTunes folder. Restart iTunes and you should have a working database but with fewer items that you can add manually. It may not be complete, but at least it will work fine. You can delete the _bad.itl file you've just renamed.
I think you may need a data recovery thing, search online and you'll find a lot,or you could look on CNET.
I think Syncios data recovery is a good choice.