Before you start investing time (or worse, funds) into a 20 year old notebook, realize that these are worth about $20 complete and working. About the only thing to try before recycling the system is to remove both the main and the reserve (CMOS) battery for 30 minutes.  If the system doesn't powerup thereafter, whatever you'd spend on trying to repair this system is better spent on a newer model.  
-Pluging in and out from the wall -plugging in and out from the laptop -Removing a battery while turning on(with the charger in the laptop) -Removing the charger(with the battery in the laptop) -waiting a minute between tries and holding the power button -clicking the power button but they did seems to help when I try to turn it on. If I have to I could try to do messurements on the motherboard and replace components if needed and stuff like that.
2003 Dell inspiron 5100 doesn't power on