Minecraft Server + Minecraft CPU Maxed Out - Java

The server started to max out my CPU, and then it started to not respond, i get a 'server timed out' error when trying to connect and when i could connect, it lagged, froze alot, it was unable to play.
It has never done this with other versions before, i even tried 1.5.2 and 1.6.0 and they worked fine.