Iphone 3 has been on charger for hours, not charging?

I just bought an iphone 3 from someone today, the battery was getting low so I plugged it in, it has been on the charger for 5 hours but is still not showing any more battery life. Any suggestions?

Un plug it then plug it in again.

Take it to the at and t or Verizon store they can fix it

They either ripped you off and the battery is fried or something similar, or it may just be the chord! Some of my iphone chords don't work and some do just try a new usb! Or it just may take a long time… After i didn't use my iphone 3G for a couple months i had to leave it plugged in for a couple hours \
also check this out
https://discussions.apple.com/...0&tstart=0

1st off there's no iPhone 3. Its either the 3G or 3GS. Sounds like the battery may have been faulty. Either try to get your money back or go to an Apple Store to see if they can help.