Going to be as specific as I can, it's a little tricky without my laptop in front of me, but I'll do my best if there are any specific questions.
I have an MSi Gx780 laptop with an i7 2960xm CPU and long story short it burned out and is no longer usable. I called the manufacturer (Gentec PC) and they recommended an i7 2640m (and the reason for the switch is because if you look up the 2960xm it goes for around $300+ for a USED unit).
I gave this to my technician and he said it didn't work, no reason (it seemed to drop in just fine) but he said the video card nor the cooling system wouldn't start.
The company who sold me the 2640m swears it was working and tested but I can't verify that. Looking online (The same links I provided above) they (The 2960xm and the 2640m) have the same socket and bus speed, the biggest differences lie in the frequency. I'm not to good with this computer build and repair business so I'm not exactly sure what makes CPU's comaptible with the motherboard, but I told it was the socket type and pin count mostly.
They are also both G2's so my biggest question is, why did the new CPU (with the same socket/pin set) not work? And what can I do to insure I get a proper CPU (besides the stock one which is just to expencive). Another CPU I saw that I think would work (G2, same socket and pin count) is an i7 2620m which has the same frequency as my stock CPU. Someone suggested it was my motherboard causing the issue not the CPU, but I've taken the computer to four repair companies and no one has said it's the motherboard, so let's assume it's the CPU. Hope that's enough information if anything else is needed, let me know!