This is a common problem and normally starts to happen when the net-book is 3 or 4 years old.
What happens is simple, when storing the laptop in it's case most of us wrap the cable round the power supply. Over time the constant bending of the cable where it connects to the power supply takes it’s toll on the insulation and it eventually breaks.
To try and stop this from happening the manufactures reinforce the cable at the weak point. Eventually the cable breaks at the end of the reinforcement. At first this results in intermittent power failures when you move the net-book. Eventually the power supply stops working altogether.
Ideally you'd replace the cable but since the power supply is a sealed unit the simplest fix is to simply repair the broken cable. Fortunately this is an easy repair which takes around 15 minutes.
Power Supply Repair step 1
Cut the broken cable at the break and carefully remove the plastic which reinforces the cable to expose the inner cable and outer shielding (earth). Twist the outer metal shielding so that it becomes a second wire. Tin both wires with solder - see photo below which shows you what I mean. Be careful not to further damage the wires or insulation when you do this (There's only about a cm of wire available and you don't want to have to cut that back any more than necessary).
Now we are going to prepare the cable ready to be reconnected to the charger. Carefully strip some of the insulation from the exposed wire as shown. Twist the outer shield (earth) to form a second wire as you did before and "tin" both wires with solder. This time you can take as many attempts as you like because there's plenty of cable to play with. Note how I've deliberately left the outer meatal shielding longer than the centre core. It's now been twisted to form an earth wire and tinned with solder. Its best to leave it overlength until the centre wires have been soldered together (see below)
Power supply Repair Step 3
Cut 4cm long sections of heat shrink tubing in increasing diameters and thread them onto the cable. This step is optional, if you don't have heat shrink handy you can use insulating tape. I prefer to use heat shrink because it protects the repaired cable better.
Power Supply Repair Step 3
Carefully solder the inner wire to the powr supply, take care not to overheat the wire when you do this since it is imperative that you don't melt the insulation. If possible get someone else to help you with this step because you realy need 3 hands in order to hold the wire, solder and soldering iron.
Power Supply Repair Step 4
Wrap the soldered inner wire with insulating tape. Cut the earth wire to length if necesary and solder the outer cable. Hopefully the repair looks something like the one in the photo below.
Power Supply Repair Step 5
Finish the repair with the 4 layers of heat shrink or Insulating tape.
Job done, if you've got a volt meter you can check that the power supply works before plugging it into your net-.book / laptop.
If you have any questions please leave a comment and I'll try and help.