IBM Thinkpad WEIRD power problem

Hey,

I've got a IBM Thinkpad T22 that's having a weird-out

The laptop works fine in general - apart from powering it on....

Without the AC adapter plugged in - it just wont boot.

I switch it on - it starts to boot and then *ZAP* it just shuts off - EVERY time... without fail.

As soon as I plug the AC Adapter in - it boots first time.

So, i thought "OK, the battery is f00ked" - but the battery holds a charge and once booted into XP, I can unplug the AC and use the laptop as normal...battery life is normal ?!

It ONLY when booting.

One thing I noticed - without AC plugged in - the initial IBM Thinkpad screen is empty apart from F1 for BIOS blah blah blah

When AC is plugged in - I get another option in the bottom right hand corner F12 Temporary Boot Device

This ONLY comes up when the AC is plugged in.

Do you think it could be a dodgy CD drive? Maybe the CD drive is chewing up voltage when booting.. as when I plug AC in - i get the option to boot from a temporary device (CD etc)

any help will be greatly appreciated.

Thanks

Take our the CD drive and try booting from battery.