Please help - Error message on Startup 'mach_kernel' (0x12)

Hi everyone,
I do apologise if this is a common problem with an easy fix; I've been searching for advice and support all week and each fix doesnt seem to work for me.

Upon starting up my macbook pro running 10.6, the apple logo appears on the grey screen, but with no spinning loading gear. After about 5 minutes of nothing, the apple is briefly replaced by a prohibit symbol, and then returns to the apple icon.

I've tried resetting the PRAM, starting in safe mode (nothing happens), starting in verbal mode (receive an error saying ".Error loading kernel 'mach_kernel' (0x12) )
and even swapping out the new RAM I installed about a month ago for the original RAM, all to no avail.

Would anyone please be able to give me some advice? I'm starting to get fairly concerned, as I've very important files on my HDD (as we all do)

Thank you in advance for any help at all!

sounds like OS X needs reinstalling. Where you running as an Admin User, not a good thing. Are you backed up? not a good thing.

If you have access to another Mac and a FireWire cable, I'd set the Mac into Target Disk Mode, startup with T Key held down, then plug them together and backup your files from the HDD.

Then when you boot off the DVD with the C Key down you want Install in Place.

Hey Kaveman, cheers for the reply!

Firstly, yeah, I'm a moron for not backing up completely and frequently.

Frustratingly, I'd already thought of the firewire file transfer tip, but my new macbook pro doesn't have a firewire port, while my old 13" macbook does. Gar!

Now I've no idea how else to at least back up files before reinstalling OSX.

Thanks again for the reply man!

Are you sure on that? There are FireWire 800 ports on all the new MacBook Pros, and they still plug together.