folder flashing when booting up?

Hi,
My brother was using his Macbook C2D with leopard, but he just tried to boot up and theres a folder flashing with a question mark? is something wrong with leopard, how can we try to mitigate this issue.
Thanks

Try holding "option" while restarting. You should be able to select the OSX. Then click the Arrow.
If that's not working, startup with the Install disk while holding "c". It will boot from the disk.

Has your macbook been making any tapping/knocking noises recently?

Not good Mr. C. When you get it booted go to Disk Utility and see what SMART verified has to say. If it advises Disk Failing, get another drive pronto.

oh, erm, apologies for.... erm... whatever... ???