Power light blinking and after 2 seconds it's off

First of all hi yesterday when I bought Dell laptop and go for home and I started my laptop d630 I press the power button and oNN then after 1 minutes it's automatically directly off and now it's on and after 2second it's off again and again so I disassembled hard-disk and ram or a battery but nothing happens I'm not quite sure my ram is okay and do not check another ram iff this method not worked so what can I do thanks