What Feldmarschall said.
Also, try plugging it in and wiggling/bending the cord in different spots. If you can get a charge while the cord is bent in a specific area, but lose the charging status as soon as you let go, it would indicate a broken wire. You can fix this yourself if you have a soldering iron - or just buy a new charger.
Before chopping apart any wires or dishing out any money for a new charger though, as suggested above, try other chargers first as it could be an issue with the phone itself.
One last thing you should try, is to attempt turning the phone on without the battery inserted. Plug it in, remove the battery, try and turn it on. If it powers on, you know for sure the charger works.
The issue may be multiple things, but is most likely the charger. It could be that your battery has bit the dust and needs to be replaced. It could be a broken connection somewhere between the charging port on the phone and the battery, etc etc.