Question Lenovo Y700 bootloop

[Adamistr0]

Hi, my friend has Lenovo Y700 and after he replaced thermal paste it will not boot. He knows about ESD, so he was careful.
When power button is pressed, LED lights on and after 3 second computer reboots. LCD does not turn on. Of course I tried removing CMOS battery, unplugging everything, leaving only power cable and RAM, but it did not help. I also tried other RAM, but it is still the same.

Anything I could do before getting new board?

 

[Lutfij]

I don't think your friend fried the board. More likely that the laptop has been reassembled incorrectly. Are you sure he reassembled the laptop in the exact reverse order that he'd disassembled the laptop? All cables and connectors plugged in and all screws mounted? Can you parse the SKU to your laptop?

 

[Adamistr0]

That's the problem, to remove heatsink you only need to remove bottom cover, so he did not touch anything. He also went to some repair centre, but they were asking price of new MB for repairing this one (without warranty..)
Besides I tried removing the whole MB from it and boot just with RAM and power supply. It still reboots. Also it starts right after plugging in power, he said it didn't do that before.
I have repaired a few laptops before, but it was mostly water damage. I don't know what I'm looking for on this one.
It is Y700-15ISK, model 80NV