Xbox 360 Jasper freezing

I get random freezing from a 2 month old Xbox 360 JASPER. I bought the unit used (1 month old) and have been testing and playing the past 2.5 weeks.

Unit: Microsoft Xbox 360 Jasper. MFG 3-25-09. 110V. No cooling or case modifications.
Usage: 1.5 months used. Have used the unit for 7 hours straight no prob.

Good news: I've been able to use the unit and fortunately I don't get a Red Ring of Death - even after a power spike.

Bad news: Occasional Screen Freezing. System becomes unresponsive. While offline play, online play, Xbox Dashboard.

What happens during a freeze: Everything stops moving on screen. Sometimes the screen darkens a bit. The controller also stays lit and the unit become unresponsive. After pressing the ON/OFF button twice, unit restarts and plays fine for at least 2 more hours.

In random areas in some games, the unit freezes, mostly during playing NBA Live 09. This may have occurred in other games as well (I don't remember), but I've only noticed this a lot in NBA Live 09, maybe because I've been playing the game so much. This has also occurred while on Xbox Live and while playing Versus against the computer.

This has happened just now after playing for 4 hours straight without shutting down the Xbox. Last night I was playing 7 hours straight before the freeze happened while playing on Xbox Live. I also played 3 hours straight, unit froze, so I go, off then on restart, then continued on for maybe 2 more hours till I just turned off the unit.

The last time this has happened during Xbox Dashboard was once, and a long time ago that I don't remember what happened. I have played AND completed other games without this occurring (50 cent: Blood in the Sand, 5-6 hours).

Possible reason: Due to the history of the Xbox 360, overheating may be a cause. There has also been a history of NBA Live 09 being so graphic intensive that the Playstation 2 could barely handle the game that the system would not get past the loading screen.

Just when I was beginning to enjoy myself. Hopefully Microsoft didn't mess up again.

-christen25