immobilizer / key fault = massive pain behind my eyes

Hello, I am a new member, although have always visited site frequently to read threads due to my ever increasing run of luck (all bad) with cars.

Anyway after giving myself a headache reading numerous different identical problems with a million different theories I thought i'd just explain my symptoms here and hope that someone could give me some answers that my fried, tired brain might be able to recognise.

Basically I had a machine in the boot of my modeo estate (2003 tdci 130) and it was a little too big so it has sat there for a couple of days with the boot open.....I took the machine out this afternoon and went to move the car but there wasn't enough umph in the battery to fire it up, so I put the jump leads on from my mother in laws diesel and went to start it and the immobiliser was on. left it on the leads for a while and tried again...same thing, tried the other plain key with the blue chip....same thing, read loads of pages on the interweb and got the code after the constant  flashing led on the clock stops, it flashes 1 then 5, so i'm guessing 15, read some more info and i'm still non the wiser really....Just seems weird it happened out of nowhere really, which is a major pain in my backside as I was given the car to help me out of a bad financial situation, then last week a nice supermarket lorry threw loads of crap on to the road in the temporary roadworks after diving into the ditch and back, wiping out 3 of my tyres (at midnight on a saturday) costing me nearly 300 to get the car home....and now this......HELP!!!  anything gratefully appreciated.....Tried fuses also, all intact