2007 Volkswagen Polo electrical problem in car

I have 2007 TDI polo. Lovely wee car to drive although having a few electrical problems atm. It originqlly started when the doors were nog working. So i got a new battery for it and i thought that would have fixed the problem. I was wrong. Recently the handbrake light and abs light come in and chime three times then it goes off then my stereo concks out and then the power steering goes aswell. So when the radio goes off and when the radio back on the mileage and the time are reset back to zero. Once i pull over and take the key out the locking in the car always goes a wee bit nuts then i ooen and close the door and put tye key back in to get it to start but its almost as if theres no power getting to the car. When the power eventull comes back it starts first time so im not having problems with it starting or anything. Could anyone give me some guidance as this is out if control or someone share any similar expierances