What happened was that when i went to open up my survival world from a 1.7.9 client to a 1.8, it was too slow to record for youtube, so when i switched it back to 1.7.9, i logged on, and my inventory was cleared, the chest was cleared, and the furnaces were cleared. I run a Windows 8 HP computer with a java version of 8 on update 25. i tried to attach the world, but it says that there is no data. There may be a possibility that the game cleared all of the data of the world.