Dead Battery or something else?

I tried to start my car the other day and it was completely dead, no sound when I
turned the key and no lights came on.  It had been a few days since I had last
driven it and it didn't appear that I had left anything on.   

It was another day or two until I could get a friend to try and jump the battery.  
When his battery was connected to mine, the lights would come on and it would
make a noise like it was trying to start.  After waiting for awhile (about 15 min) and
still getting nothing more than the lights and the sound.  We disconnected his
battery from mine and everything was completely dead again... no lights no sound
no anything.  Does this mean I need a new battery or did we need to let it charge
longer?  

Please help!