Taking the battery out/putting it back in may help but to do a proper power reset you should:
- Unplug everything from the laptop (power, pen drives, external devices, etc etc),
- Take the battery out,
- Hold the power button for 15 seconds,
- Attach the power cable
- Try to turn the laptop on (battery still removed).
As the adaptor light is on it's neither the plug nor the socket, but it could still be a problem between the adaptor and the laptop. The only way to test this is to try a different adaptor with your laptop, or a different laptop with the adaptor. You could also try a multimeter if you have one. If none of that is viable then go into PC World and tell them you rang up and were told to take your adaptor in to be tested. They'll tell you whether the adaptor works.
If the adaptor works then the problem is with the laptop. It could be the ac socket - check that it looks OK, that the pin isn't bent and the socket isn't loose. Check the other ports on your laptop as well - it's been known for damaged USB ports, for example, to cause these symptoms.
If the ports are all fine then the problem is internal. If you're lucky it's a wire, if you're unlucky it's something like a fried motherboard. There's no more diagnostics you can do without opening the laptop up.
All of the above assumes that when you attempt to turn the laptop on absolutely NOTHING happens. There's no noise and no lights on the laptop. Pay close attention when you press the power button to be sure of this.
If there is some sign of life then things are different. If the light comes on and flashes, or the laptop beeps, then it could be an error message. Let us know exactly what you see/hear. If the fan comes on but then everything goes silent it could be somethinhg like overheating. If the laptop light stays on then it could be a problem with the screen, or the laptop could be stuck in power saving mode (amongst other possibilities).