Is there a way to completely stop & lock a Win7 laptop hard drive and at the same time use the laptop ram to play an audiobook while driving?
it is called an iPod. Running an OS in memory is a really fragile task. Get a SSD or buy a $40 12V>>120V power inverter. What you are asking is possible - but it is one of those "if you have to ask you can't (afford, understand, pull it off, etc.)" type things. Do you have a reason for wanting this other than not draining your laptop battery?
It seems that playing an audiobook is not a good reason to use a laptop in the car. You need to flip up the screen and such. How about some iPod-like devices? I am sure they have made some playback devices that takes audio files from a USB thumb drive or a SD card or sync-up/download to it via a USB port.