Why does my laptop say, charger plugged in, not charging?!?!?!!?

I sent my laptop to boston about 3 weeks ago to get it fixed. I get it back and the charging part has all been fixed and its basically brand new. I get a charger and plug it in and it works FINE. two weeks later ( yesterday ) i turn my laptop on and i see that it says that my laptop is plugged in....BUT NOT CHARGING. I didnt do anything to get it to be like this. Please someone tell me how to fix this problem whitout having my parents knowing. I have a Dell Inspiron 1545. My laptop has currently 95% l;eft in it with the charger in. Please someone tell me how to fix this. My charger is bran new!! idk why this is happening! My battery life cant be low because i checked it. Someone please tell me how to fix this! thanks!!