Vauxhall Vectra loud clicking noise and crazy electrics

I started the car the other day and it struggled a bit like the battery was maybe a bit dead, but it started 1st time and drove home perfectly fine, however, the next morning as i started the engine, the engine didt start and instead, major clicking noises coming from the engine, and all my electrics went haywire,

ie... cd player started flicking through all the cd's the screen told me to check rear indicators then press ok, then it said nothing else, i turned the key again and the same thing happened, If i have the ar door open whilst trying i can hear a slight hissing noise underneath the car but only when i stop trying to start the engine, also i then got out an tried to central lock the car...?!?! 1 front lock and one back lock went down and the other 2 stayed up and each time i pressed it different lock went up and down and the alarm kept going off??! i ended up manually locking all doors and its now sat up the drive, as its been weekend and no where open, anyone have any idea before i go to a garage an make a fool out of my self as im a girl if its something really simple id like to know haha!! thanks