Samsung Galaxy S — Lots of things went wrong all at once, please help?

So I turned my phone on yesterday, and it took longer to turn on than usual, and when I turned it on none of my apps were on display and all settings had been reset. I had to put everything back where it was.

It the turned out all text messages had been wiped, all contact photos and contact name changes that weren't saved to the sim, and all memos gone.

Also, the home key stopped working properly. Somehow, plugging into my computer fixed the home key (for now) but I still don't have any of my messages or anything.

If anyone has any idea what might have happened or how I can get back my messages and my memos, it really would be appreciated because there's a lot of stuff in there I need ^^;

Thanks!

I don't know, basically all I did was turn my phone on, unlock it, turn the screen off, put it in my pocket... Then when I pulled it out again it had switched off, which I assumed was because it was out of battery, and when I switched it back on again everything was gone ^^;

And I have no idea what that means >.<