How do i know if it's the battery or charger thats bad

Have you pulled the battery out of the system?  There should be a button on the side of the battery that you can push and see which of the 5 lights come on.   If one of the lights just barely comes on when you hold the button down, it sounds like the battery is drained.  You've just got to figure out why!  With the battery out you can try the system with just the A/C adapter. 

 

It almosts sounds as if the system is not getting power at all.  I would check the A/C adapter and make sure the cords are plugged in firmly.  On the power cord there should be a box, make sure the A/C cord going into that box is seated well.  Additionally try plugging it into another outlet to make sure it's getting power.

The battery is dead will not charge, When i plug in the AC the 3 lights in front flash for a sec.and then and then the one on the right blinks every 15 sec.

Do you have the same flashing light with the battery out?

I would recommend removing parts, one at a time to see if the system will power on.  Start with the easy ones.   I wouldn't go

as far as to remove the mainboard, processor or system fans.   I would however remove the hard drive, memory modules, optical drive, keyboard ect. 

 

Be sure to ready "Before you remove or Replace parts" before starting to tear down the system.

 

Here is a link on how to remove parts:

http://support.dell.com/support/edocs/systems/ins2600/en/sm_en/remove.htm#1103387