Macbook Leopard 10.5 is not booting up and not even getting Verified Error : Invalid Node Structure

Hey, I am using Macbook Leopard 10.5, Yesterday while i was working it was on low battery i thought to connect it later, but all of a suddent its stopped fucntioning and everything goes blank. I thought it might be a Battery problem, but even after connecting charger for 2-3 hours, its not booting up. Only the Apple screen comes and then it goes shut down automatically.
I even tried to fix it using Apple CD, Disk utility, When i tried to Verify the disk It shows following error :

Disk cannot be repaired or verify.

And details : Invalid Node structure

Volume needs to be repaired error : Filesystem verify or repair failed.

I have very important Data on this disk, so i cannot even erase it.
Suggest me somehting. It have enough space to install new OS but System shows you need erase it.

I have tried to use Apple Hardware test by Holding D key, But its not working.