Help what could be wrong With My Car

Its always started first time and I popped out in it tonight, all fine come rushing indoors and then straight back out to go somewhere else. Put key in ignition and nothing. All the dash lights went out as I turned the key and it won't do anything.
I got out and tried to lock it and the central locking sounded so slow I panicked and unlocked it straight away again.
It only very slowly just managed to unlock my door, the others did not unlock. So now I darn't lock it or I won't get in it again.
Don't think its the battery as its a really good battery and had only 15 mins previously started the car first time.
Its an R reg Vauxhall Astra estate 8 Valve.

Just asked Dave for you, and he said it could be the alternative which has NOT been charging your battery Bev. You need to get it jump started and take it from there, or take it to the garage once it's started maybe? Not much help is he! It could also BE the battery he said even though you think it's not, but it's more likely that the alternative has packed up and consequently hasn't been charging the battery and you've only been running on what's been in there. Overnight it usually gains a bit of charge, enough for you to start it, but then it might conk out on you again I suppose if he's right?

I think you mean the Alternator not the Alternative don't you LOL .
May be but I had that go about 18 months ago and got a warning light come up on my dash. This time it seems different.
I wondered if something has blown a fuse somewhere or shorted out as its seems more electrical if you know what I mean.

Lol, yes, I'm having puter probs and that's what it does to me!

Dave just said it could be anything really. If it were me Bev, I'd think back to what I did when I switched it off when you dashed indoors, you could have inadvertently done something??? Good luck!

I've just had the AA out and its my battery. I didn't realise it could go that quick. But he tested it and definitly battery. The alternator is fine he said Phew.
Thanks for your help.

I once went to pick up my wife at work. With the engine warm, the car sat about 10-15 minutes. When she came out, it wouldn't start. It couldn't be jump started. Even after being on a charger overnight, it was still dead. We had to let it set until morning and put a new battery in it, before it would start. They can totally fail with no warning.