The ideas and suggestions to date are good
Also try removing all USB devices before starting and
Also try connecting an external monitor
Also try turning it upside down/sidewise and see if it starts (soldering problems, foreign objects etc.)
- also try swapping the power adapters and batteries between the laptops just for completeness (doesn't seem likely but check anyway)
If you're seeing no boot screens / info and no bleeps either then a main board power, main board, CPU or bios problem is likely (most PC's will happily boot without a CMOS battery but date /time/region/keyboard info are unavailable until windows is up.
Assuming you can get to the HDD I personally would remove it, stick it in a USB caddy, connect to another PC and if it's accessible make a copy/backup of any valuable data etc before things go much further.
If the drive data is not accessible that might be, or itself be a victim of , the problem... (note that a failed HDD will usually have been be reported via obvious Bios warnings about faults with / lack of a system/boot drive)