Because of excessive heat… your xbox 360 freezes…
…want to know more?
It’s freezing up is a huge warning sign you are about to learn what the red ring of death is and how it effects 360 consoles.
Inside your xbox 360 is a massive amount of heat. And it uses certain mechanisms to cool itself.
Heats sinks move the heat away to prevent over heating the mother board. It needs a way to remain cool and one of the ingenious ways Microsoft uses to keep it cool is by soldering heat sinks to the mother board.
The heat is removed from the system internally with a small fan inside and the heat sinks help reduce temperatures.
The reasons it may be over heating and freezeing are:

1. The soldering joints which were used when it was assembled were not the most effective material they could of used.They become worn down through hours of exposure to the heat and slowly loosen. As they become loose, the heats sinks stop removing heat from it and everything starts to freeze up.
2. The fan inside stopped working and causing it to over heat.

I can almost bet your xbox 360 freezes after a few hours and  it begins to over heat. And you might be heading for some more serious problems if you don’t get it fixed as soon as possible.