The laptop may not boot up for a number of reasons. CMOS battery could be one reason.
Check if power light lights up or blinks. Check if you feel any vibration. Check the air vents if you feel air blowing. If you hear any beep sounds, note if it is short or long beep, single or double beep, etc.
Sometimes this helps - remove the battery, then press + hold the power on button for some more seconds.
Once you have some indication from above, you can google search that and fix it yourself if you are confident. If not call for professional help.
If there is simply no indication at all, and your power supply point (from wall) is working fine, then your motherboard is dead. Again you should be confident of your abilities to try to fix the MB yourself but this is not a simple matter. You need some specific tools and knowledge to do this part, and still you may not be successful in the end.