Vauxhall Vectra starting & electrical problems

Just aquired this vehicle. (Wish I Had not!!)Out in the morning (Freezing Temp) car starts first time, two hours later and it refuses to start. It will turn over and over and eventually the battery is dead. I then have to rely on my other half to rescue me with a set of jump leads!!While waiting in the car the other evening the interior light was coming on and off on its own although I was not touching anything?? There appears to be no common denominator. It may start every time or it wont start at all. Cold or warm engine makes no differance? I also have a problem with the electrics although not so bothered about that. Going along and the speedo and all other clocks drop to Zero but does not affect the cars performance. I have discovered that if I open the drivers door while the clocks are down, they come back? (I am thinking the car must be haunted) Please can someone offer any advice? I would be very grateful. Thanks