We professionally repair XBOX 360s using factory repair methods. We use expensive rework/reflow machines with detailed and unique profiles specifically for the XBOX 360 CPU and GPU
This method (IRDA/HOTAIR rework/reflow) is a Electronics industry standard used to attach and repair devices built on  BGA (ball grid array) architecture like laptops,cellphones and XBOX 360 and PS3 etc... more on BGA here
Fixes rrod(red ring errors)  e74 errors, no video etc....  

Even if another has fixed It and it broke again, There may still be hope.  As a matter of fact we get alot of "redos"  because the boxes are not fixed properly the first time.
What we do is reflow the bga/chips with a rework/reflow machine. This is an actual factory repair method not just some xclamp fix (which most people do)

Beware there are alot of hack fixes out there on the web that range from overheating the box ( by wrapping towels around it, all this does is warp the board and damage it even further) to putting pennies on the chips, to just a xclamp fix that just mashes the chip under pressure back to the board, which will fail again once the board goes through its heats cycles of heating up and cooling down. 
Be careful who you choose to repair your xbox, some will claim to do reflows but use a heat gun ( the kind used to remove paint or wall paper) to try to accomplish this. All they are going to do if you are lucky is nothing more that warping the board much like the "towel trick" or an xclamp fix as described above and temporarily make bga connections to the motherboard again.  For those of you that are unlucky they will more than likely destroy your chips through thermal shock to the components.  
Some people offering repairs services ( and people doing it themselves at home) can actually damage these so they are not repairable anymore.
We actually have and use a rework/reflow machines! Not some hotair gun or some rigged together thing off the internet!
Reflow machines are expensive and require not only skill, but a detailed reflow profile of temperature and times unique to the xbox chips to ensure the chips are not damaged by increasing/decreasing the temperature too quickly and to ensure reflow of chips. There is no way to do this otherwise
We have a proven profile that we use and validates reflow
This should only be done if you box is out of warranty and you understand the fix MAY NOT be permanent,

However with the correct cooling we have found 97% ( some are just too damaged) seem to last for up to a year and counting
I recommend :
We can do a internal 12 volt fan mod for free which will have the fan running at full power always. This keeps the box considerably cooler  by 20-30 degrees


 Cost of repair is only $35
We also do DVD repairs, open tray errors etc.... Contact us for price