my car wont start?

I have a fiesta 1.2 on a P reg, when I went to start the car in the morning it wont start, when I turn the ignition it ticks over making a tapping noise, with the dashboard lights being very dim as though the battery is dieing. I tried to jump start it with another car but it does the same thing, wont start!! I even taken off the leads off the battery for 5 minutes so the CPU can re-configure it still wont start! There are no visible leads that are loose and checked the fuse box still no joy. What could be the problem, if anyone has any suggestions please do share.