Welcome, Newcomer. You're going to have post more info regarding your trouble and include the model number of the laptop, too. However, the power trouble could be related to a number of things.
To start, try removing the battery and leave the plug in. Turn on the power, does the system stay on longer than 15 secs? If yes, you possibly have a bad battery.
If not, continue diagnosing by removing the panel that covers your CPU/heatsink. Clean out any excess dust build-up you may find.