Although the charger may seem fine, the do break down, without showing any physical sign of problems. Seen this many times. I would be sure to try using a different charger cord, or test your cord on another device. If the cored works on a different device, it isn't your cord.
You may also want to check the battery to make sure it hasn't died. They do go after a while. If you have a similar device, or know someone who does have the same battery, try theirs in your device or vice versa to see if it is your battery. If it is, replace the battery.
It can also be a problem with the port in the device. Check to make sure it isn't dirty (has dust, etc., in it) and also that it isn't loose. If it is, you may need to have it (and possibly...