ITunes deleted all playlists and purchases

Question

Help!
The other day I closed my iTunes program and it was working perfectly. I came back a few minutes later and re-opened it, only to find that all my playlists, purchases, everything had been deleted! All that is left is a library of songs about 3 years old. None of my activity (i.e. loaded songs, albums, purchases, etc.) since then is on there anymore.
I'm not computer savvy, so if anyone could break down some super simple help for me, that would be amazing!

Answer 1

It sounds like something has happened to your iTunes Library files - default location C:\Documents and Settings\User Name\My Documents\My Music\iTunes - which in addition to telling iTunes where the actual song files are located also contain playlist and related information.
If you don't have a back-up copy of the last "good" .itl file - which would restore your Library - there are a few options for you to consider:
1) Search your computer for any and all of the .itl files it contains. Each .itl may contain references to a significantly, or completely, different library and following the steps described in this article in the Apple Knowledge Base, you can check them and may be able to reconnect iTunes with the particular Library that you're looking for. Close iTunes for a half minute or so before restarting it each time you want to choose a different library file.
At this stage, skip any of the .itl files located in the Previous iTunes Libraries folder ... We'll get back to those, if necessary, in Step 3).
2) You can rebuild your Library with the procedure outlined in this article in the Apple Knowledge Base.
You will lose some of your playlist related information (playcounts, dates added, dates last played, etc.) - but will retain most of it (ratings, comments, etc.) - with this method. The actual contents of the Library should be up-to-date.
3) If you don't like the idea of losing the playcounts and such, have a look at this Knowledge Base article for one other option.
Using this method will restore your iTunes Library to the exact state it was in on the date of the most recent .itl file in the Previous iTunes Libraries folder. The drawback is that any changes made since then - songs/playlists added and changes in playcounts, ratings, comments and such - will not be included in the restoration. But it will be easy to add newer songs by following the instructions linked to in Step 4).
4) One final option is starting all over again with your iTunes Library by following the instructions in the Add to Library section of this KB article .
This will update iTunes with a list of all the files you add but will not maintain any of your playlists or related information.