Before I take my Macbook Pro in to the shop does anyone have any ideas on this problem that has just started happening?

When I plug it in to the mains the power light is green but never seems to charge ie when I unplug the power it swithes off instantly. I've tried taking the battery out and replacing it, tried switching on without the power cable (nothing happens).

I don't know anyone with a pro to use their battery.

Any ideas?