Usually these are two main reasons. 1. Your charger has an issue and not really charging - Fix: try with another Dell machine from your friends or relatives or use a spare cord to test if it indeed charging. 2. Your power jack on a computer side has an issue. In that case you have to know how to fix it because spare part (computer jack) is cheap but you have to open casing and replace it and if you don't know how, you have to ask someone who does know. I do not see any other case when your problem could happen except, and it more speculation then the true case, your operating system is giving you issues and not properly showing that there is a charge. Also, if you see a red cross on your battery sign that means a battery is dead and does not hold any charge at all.