Punto electrical & immobiliser problem, Can I bypass it?

I recently bought a Punto on a 97 year (about 2 weeks ago). I seemed ok when I got it and it drove fine for a few days, however over a period of the first 2 weeks it developed a number of issues. I became difficult to start and sometimes it wouldn't do anything when you turned the key. Driving at night became a nightmare as the lights seemed to drain the battery to the point of cutting out, the speedo and rev counter temporarily stop working, dash lights dim and the key code light flickers along with the injector light, but picked up for a short while if the lights were turned down, so I changed the battery as it seemed not to be holding charge and it seemed fine for 2 days until it did the same again. So I checked the brushes on the alternator which were fine as were all the connections. I've charged the battery and it turns over strongly, however it won't fire up. I have a feeling that the immoboliser has reset itself and i don't have the original red key. Can the immobiliser be bypassed? Can anyone help with the failing electrics? I think i've tried eveything obvious...