My Xbox is just "freezing", no RDOD, whats wrong?

When I first turn on my Xbox, it runs fine until you start playing a game. Five minutes after game start, it just freezes, no RDOD, Xbox button on the controller does nothing. I have to turn the unit off to get it to respond again. I have already cleared the System Cache in hopes that would fix the issue but to no avail. The Xbox is no longer under warranty. I already have it dismantled on my bench, i just wanted to know if a re-flow will fix this? Any idea's would be very helpfull :).

Cheers :)