Boxster won't start! Funny symptoms

[brewnog]

Hi all,

I've been reading this forum for the last 3 happy, trouble-free years of owning my 2001 Boxster S, but unfortunately now have cause to ask for help!

My Boxster won't start. Everything lights up, but it won't crank.

I've had a funny few symptoms over the 24 hours running up to this, and I'm wondering if they might be related, or completely coincidental.

Yesterday, my window winder mechanism packed in. The motor sounds like it's crunching. I've stopped using the window, but obviously every time I get in and out (or put the roof up or down), it's trying to use the motor, so 'crunches' a bit.

On the way home today, the car was going really well. I got stuck in a traffic jam for quite a long time, but had the roof down, and heater on full blast. During this time, the radio suddenly stopped working (it had the power to eject a CD, but won't switch on). Also, my airbag warning light came on about the same time. I've had problems with this in the past, but these were fixed (until today apparently).

The rest of the journey home was fine. I put the hood up (cue window mech crunching), and switched the engine off as normal. I then decided to see if I could get the radio to come back on. At this point, the engine would crank, cough into life briefly, and then not start.

Wondering if everything had just got a bit hot (traffic jam!), I left the car to cool down. I went back to it later, and now, it won't crank at all.

All the dash lights come on as normal at key position 1, but the only noise I get at the 'crank' position is a tiny little click behind the ignition key (relay in the dash somewhere?).

I thought I'd disconnect the battery to see if anything would reset. Now, I knew about switching the ignition on before disconnecting the battery, so I did this. However, the alarm still went off, (siren only, no horn).

I'm wondering if I have an immobiliser problem? I've tried connecting a (known good) battery in parallel but it made no difference.

Any other opinions on what to check would be very gratefully received! I have a multimeter but no digital diagnostic equipment.

Thanks in anticipation!