Problems with MagSafe

When i plud my MacBook Air to DC using my 45W MagSafe powersupply, the plug often lights green. I read that this was because the batteri was fully charged, but in my case it in not ..

If i mess a bit around with the plug, maybe reattach it a few times, i can almost always make i light orange (charging), but if i touch i just a little bit, it goes back to green again; and the charging stops..

Do you think there is any ways to solve the problem - or should i simply buy a new powersupply (or a new Air?) in order to fix the problem?

Thanks, D_D