Chosen Solution
why is that my power adapter is sometimes not charging then after some few days it would charge again?
Is the cord damaged? Often I see people winding the cord around the studs in such a manor as to put a twist into the cord its self. Think how the flat phone cord gets spiraled around its self. Over time this stresses the wires inside so they break. When you release the tension the wire ends can sometimes joint backup completing the connection. Apple also changed the way the MagSafe connector was attached to the cord. Make sure you have the newer type charger for your system. If the cable at the connector looks messed up Apple will give you a new charger for free.
