My Dell D600 Laptop will not power on anymore

I have been having problems with it for a couple of months now. when I turn it off it was hard to turn back on. sometimes it had to set for several hours with bat out and power cord unpluged. I turned it of about a week ago and can’t make it come back on. When it worked, if you simply restarted it, it powered back on fine. Bat is fully charged and power supply is supplying proper voltage.