friend has a 12" g4 ibook, purchased in august
she put it to sleep, took it for a ride in a cold car, brought it inside, tried turning it on, nothing. no whirr, no bong, no screen. removed battery and AC adapter, put them back in, still nothing.

let it warm up to room temperature, nothing
tried removing batt and power adapter again, nothing

any ideas?

It's likely that condensation might have fried something. You should NEVER immediately try turning on an electronic device after a major temperature shift like that. You should always let it warm up to room temperature first. Since the iBook should still be under warranty, it would be best to try having it repaired that way.

I brought a computer in from a cold car (where it sat all night ) and blew the power supply once it was plugged in. Always let the computer warm to room termperature before plugging them in.

not does that rule apply to computers, it also apply to any electronic....

Uhh, yeah, that's what I said above:

Wow I had my iBook in the car last night for 8 hours and I turned it on soon as I got in the car. Thank God that didn't happen to me.

this is what happened to my i-paq when i left in over night on the car by accident but what i tried doing was heating it abit and then removed as many parts as i could then put it all bak togetheronce warmed then it worked

That would be fine, so long as the car was still cold. The moisture in the air would only condense if you took the iBook someplace warmer than where it had been. The humidity level of the air plays a part in it too.

well.. so much for the thought of some advice on what to do..

I would take it to an authorised repair place or call apple for it.
It should be covered by the 1 year hardware warenty.

Unless you have issues with apple support as I did.
It took my one month to get them to send me my stupid repair box...
But I will not get into that story .. Unless anyone wants to hear a long and sad story.
Though I should get my box to send the laptop in today ... after a month of phone calls

My first reply told you exactly what to do. Have it serviced under warranty.

Maybe he want's a second opinion?

I think you should take it in and get it serviced by a genius.

They'll tell you whats up. What's even more grand is that you're still under warranty, so it's a win-win.

Listen to ROADWARRIOR!

resetting the PMU (CMD+SHIFT+CTRL+POWER) fixed it