Expert help needed!!

PLease help if you can!

My Macbook started playing up, for no reason.

It was working normally, then suddenly it was unable to detect any wi-fi networks.
Then when I turned it on, for no apparent reason it started asking for an administrators password....which I have never had, so I couldn't login.

I tried creating a new user....following procedures suggested on here, which didn't work.

Then the damn thing gets stuck booting!
It spends ages on the grey screen with the apple icon on, then eventually it goes to the blue screen, then is stuck there. I am unable to shut down without removing the battery.

I can't boot in safe mode either.

I have tried booting in Single User mode........all seems to be going ok, until I get a repeated message of "Waiting for Metadata Server".....so I am assuming it is stuck here and won't boot beyond this point as it is constantly waiting for the server.

I have tried fsck, but this doesn't work, it just displays "The Volume Macintosh HD could not be repaired after 3 attempts" .

Is there anyway I can bypass the 'Searching for Metadata Server" stage, so that it will boot?
Or does anybody have any other suggestions?

I don't have the original disc so can't reload, and besides I do not want to lose any of my data....music, photographs etc.

Any suggestions would be gratefully received.
Many thanks.