You have provided too little information regarding the issue that you have, so I find it hard to troubleshoot the case that you have. Please, give me more details regarding the issue and tell me what happened.
You should be able to power off the laptop by either unplug the power button or pulling out the power cable. My suggestion is to take out the battery too. Wait for some minutes for the electricity to discharge and if the laptop is out of warranty, open it and pull out the CMOS battery. Wait for some mins more and plug it back in. Then plug back the power cable and the battery and try to start over.