The charm of a notebook computer is you can easily
Bad Battery
Sometimes the battery refuses to take a charge because the battery itself is bad. Whether it is prematurely defective or several years old, a bad battery will refuse to charge. Replacing a bad battery can be expensive, with after market replacements starting around $100 as of the time of publication. If your computer is still under warranty and it has a bad battery, contact the manufacturer to find out if you can have the battery replaced under the warranty. Otherwise, use the age of the computer as well as the cost of the battery to determine whether it is worth replacing.
Bad Motherboard
As with batteries, notebook motherboards can start malfunctioning with age, though some are also prematurely defective. In these cases, the portion of the motherboard that relays power from the DC jack to the battery no longer works. Unfortunately, this also requires you replace the entire motherboard. Motherboards are normally covered under manufacturers' warranties, so if your warranty is still valid, you may be able to get a free fix. If the notebook is not covered under a warranty, though, the cost of the repair is rarely worthwhile, as motherboard replacements -- once you factor in parts and labor -- often cost more than the notebook itself.
Bad AC Adapter
If your AC adapter is faulty, your battery will not charge properly. Minor internal breaks and fractures in your power cord can cause power to intermittently get to your battery, while a dead AC adapter will force your computer to run on battery power until the battery completely loses charge. The power cord is the easiest notebook part to replace, as many universal adapters are available for purchase. While a replacement AC adapter is still expensive, it is significantly cheaper than having to replace a battery or motherboard.
Troubleshooting
Troubleshooting a battery that does not charge is rarely a do-it-yourself task; without the right tools and knowledge, the only element you can test yourself is the AC adapter. You can do so by removing the battery from the notebook computer, plugging the notebook into the wall and attempting to turn it on; if the laptop turns on, your AC adapter is functional, but if it does not, the AC adapter is faulty. If your AC adapter is functional, the next step is to take your computer to a certified technician to figure out the exact reason -- or sometimes, reasons -- why your battery is not charging.