Laptop will not turn on

I tried thating the battery on and unplugging power cord. I held it upside down for 30 secs and couple of times. Put the battery back in and plugged power coed back in. But no go.I have a compaq presario V6000 running vista. The lights come on but the screen is black, the fan comes on for about 2 secs,it tries to boot up then it starts to turn on and off. Is there any reset I can use? Is there any button to hold down while powering it up?Would it be the motherboard?Any help would be greatly appreciated. Thanks