Remove one memory stick if there are two. Test.
Swap the stick back and remove the other. Test.
Unplug AC adapter and pull out battery.
Hold power button down for 10 seconds. Then press it again multiple times over 20 seconds.
Put battery back in and plug in AC adapter. Test.
If that fails you may be down to removing processor heat sink, cleaning off the thermal compound, putting on new and re-seating processor.
"Living tomorrow is everyone's sorrow.
Modern man's daydreams have turned into nightmares.