Current BIOS has support for i7-640M - https://browser.geekbench.com/v4/cpu/11032077
Try this algorithm with native BIOS:
1) remove AC jack, Main Battery, and CMOS Battery
2) remove HDD and all DIMMs
3) install new CPU
4) wait 10 mins
5) press and hold power button for 30 sec.
6) install CMOS Battery and one DIMM only, inject AC jack (without Main Battery!)
7) try to boot your laptop.