I've had that problem a couple of times, and it sucks, but it makes you better. Instead of focusing on the past, you're forced to move on to advance your style.
Example: Compare my second song, An Epic Trip to the Store, with Surge of Panic. Because I lost my early songs (the first 4 or 5), I had to move to the next stage. Then, I got a new PC, so I had to move even further. THEN, I got more instruments, etc.
Surge of Panic was made both with newly found preset instruments and new instruments at my disposal, and I didn't focus on my old stuff so much that it would be harmful to my progress.
Now that you've lost your old files, redownload FL Studio (or get it from a friend possibly, though I'm not condoning pirating, but I'm certainly not saying I've not done it in the past). Make a new song using completely new instruments that you've never used before.
Chdonga
Pirate.
Xarosas
umm....huh?
is that a suggestion or an accusation?