The diagnostic led “cpu hot” flashes a red light，can not boot. and post-code led is no display.
But the memory ，Graphics card，fan，radiator connected properly. and fan is work fine.
And the machine worked fine before once replace the silicone......
Is cpu or board broken ? If ture which one is it
looking forward to a reply Ths！！
I suggest that you remove the processor and then install it again. Also remove the memory DIMMs and then insert them again, ensuring that they are properly seated.
Hope this helps,