Open Question: laptop charger isn't working?

i have an acer laptop and i've had it since about the middle of october..and i've only used it a few times since then like twice in december and and twice in februrary...and now its the summer and i get to use it a lot but when i have the charger plugged in it says "plugged in, not charging". why isn't it charging the battery, and how can i make it start charging it? thanks in advance :)