R51 2887 NQ2 Thinkpad (not

Question

R51 2887 NQ2 Thinkpad (not under warranty) not powering on.
The problem appeared 3 months ago for the first time, but going through
some forums, the problem got temporarily solved by removing the battery
and repeatedly pressing the power button and then running the laptop on
AC power without batteries. But now the laptop is recalcitrant to power
on.
I have tried changing the BIOS battery and powering on the laptop without the memory module and the hard drive. Without Success.
I am disinterested in replacing the system board since I had the same
problem in warranty and got the systemboard replaced but reappeared
just after 4-5 months after replacement.