Mods and items dissapearing

When I started a new world in minecraft 1.4.2, I was excited about the new version, so I did some exploring. When I made a chest to store some items in it, I left the little house I made to get some cows for leather and food. When I came back I put the cows in my farm, but then I saw my chest was gone. So the first thing I did was relog, because I thought it was a bug. When I came back my chest was still gone, but all my cows dissapeared aswell! So now I don't have my items anymore, and my cows are gone. Could you guys at Mojang help me with this problem?