How do i fix my over heated lava lamp?

My little brother left my lava lamp on all night and day and now, half of the lava is flat on the bottom and the other half is floating on the top. The lava ended up cooling that way and now i can't get it to bubble up. When the lava melts, it just stays flat on the bottom. the coil is also flat on the bottom where it should be. I bought it from wal-Mart about 3 months ago.