I would suggest attempting to start up your MacBook using the DVD Installer that came with it.
To do this, turn on your MacBook - but don't worry about the flashing question mark, and slide in your Mac OS X Installer DVD.
Shut down the MacBook by holding the Power button down for 6 or 7 seconds.
Now start it up again, and immediately hold down just the C key on your keyboard and keep it held down.
This forces your MacBook to start up off the Mac OS X Installer DVD, instead of its Hard Drive.
Keep the C key held down until you can see both the grey Apple logo and the little grey spinning mill underneath it. Then let go of the C key.
It may take a little longer to start up, so have patience.
When it does start up, you'll see a blue screen and a panel asking you to choose your language.
Just press the return key on your keyboard once.
It will then present you with an Installation window.
Completely ignore this window and click once on the very top menu item named: Utilities - and scroll down to: Disk Utility, and click it.
The Disk Utility window will open.
Look at left panel, and click once on the Macintosh HD icon, to highlight it in blue.
Then look to the right hand side of the window, and click once on the Verify Disk button.
It should then begin examining your Hard Drive. This shouldn't take more than 2 minutes.
It may present things that are wrong with it in red text, in the window just above the Verify Disk button.
When its blue progress bar stops, the examination has ended.
Next click once on the Repair Disk button.
This should now repair whatever problems it found the first time round, and if it repairs them successfully, it should show you this, as green text at the bottom.
If however, it produces red text again and ends with something about it not being able to repair the Macintosh HD, post exactly what is says back here.
If it passes with a successful repair in green text, click once on the Verify Disk Permissions button to the left of the Verify Disk button.
This might take just a little longer, yet when it has finished, click once on the Repair Disk Permissions button beneath it.
When it has Repaired Disk Permissions, and Verifying the Disk has come back as a positive in green text, click on the top-left menu item: Disk Utility and scroll down to: Quit Disk Utility.
Next, click once on the top-left menu item: Installer and scroll down to: Quit Installer.
Next, three other buttons will appear. Simply click on the Restart button, and your MacBook should restart normally.
Once fully restarted, you can eject the Mac OS X Installer DVD by clicking on its icon and dragging it down to the Trash (which will turn into an Eject icon).
If the Disk Utility reported that it could not fix the problem, and shows this in red text, make an exact note of what it said, and repost that info here.