when I switch on my laptop, it normallyboots , but suddely shuts down

when i switch on my laptop it boots up normally. it has a battery and shows fully charged. but when i switched off my power connection, it shuts down within a few minutes. Again i switched on my power connection and my laptop. it boots normally and works fine for sometime and again shutsdown abruptly. So i removed the battery and working with powwer adapter only. It is working fine almost from so many months except rarely shutting down when not kept idle for 15 minutes or longer. But suddenly from yesterday it booted normally, but shutdown immediately. It happened 4 or 5 times. So i opened the case and cleaned inside. but now it permanently not opening, no power light nothing. Any help is most appriciated