AC Adapter

If you're not willing to purchase anything, you'll have to borrow a compatible Dell adapter from a friend to try.  If it works, you will need to buy a new AC adapter, assuming you're out of warranty.

If the other adapter does not work either, you're in need of an internal repair to the system - either the power jack or the mainboard is faulty.

But it worked FOUR DAYS AGO.  How did it just become faulty?  That doesn't make any sense.  
I'm not trying to argue with you.  I appreciate your help; I just don't understand how my power cord can just decide to give partial power.  
(When it is plugged in, the computer recognizes that it is plugged in, and I don't lose battery power, but it doesn't charge.) 

For the same reason a light bulb that worked four days ago - or a toaster, or anything else electrical -- can fail today. 

Anything electronic can fail at any time for any one of a host of reasons.

EJN63, 

While anything electronic can and will fail at any time for any reason, you miss the point. I have read so many posts about the same problem from different users and the Dell support community keeps sidestepping the issues.  I spent 22 years as an electronics technician, including computers. I have owned Tandy computers (dated myself there), HP, Dell, as well as built my own machines. Dell has been the only computerI have had issues with. When the same issue keeps popping up on the same or similar type of machine from the same manufacturer, the issue is quality of the product and that is what has people hot about Dell. I have had an HP machine for six years and never had a problem.

Not sure if you work for Dell, but it sure sounds like the company line.

I have had an HP machine for six years and never had a problem.

Obviously, you haven't been reading the HP forums.

PLENTY of problems there.

Just because you had no problems with your HP, does not mean all HPs are great.

http://h30434.www3.hp.com/t5/Notebook-Computers/ct-p/Notebook

Gee, there is even a special forum for Lockups, Freezes, and Hangs. LOL.

I realize that not all machines are perfect. But there is a reason I don't go to the HP forums ... wait for it... MY SIX YEAR OLD HP WORKS! I went to this site because my 2 year OLD Dells have issues. What part don't you get about that, IEEE488?

"emilyvandall"

below is a video that might give you some insight how things work.

I have to agree with "ejn63" : electronic parts can fail for whatever reason.