Phone not responding - think I deleted something critical/locked

Samsung mobile SGH-J750.How to get back wallpapers, locked items, etc which I deleted to clear memory on the phone.Now when I switch on the phone, it goes on with Samsung-detailed screen, followed by Vodacom-screen, and then a blue-blank screen, then a black background, whith a picture that looks like a sim-card, and nothing responds, I can't even switch off the phone - please advise me ASAP!Thanking youMarjorie