Macbook, Boot, white screen

Hi,

This afternoon when I tried to boot my macbook I had a white screen.

I tried these sequences:
http://docs.info.apple.com/article.html?artnum=303124

Result:
- Press C during startup: doesn't work (always a white screen)
- Press D during startup: doesn't work (always a white screen)
- Press Option-Command-P-R until you hear two beeps: more noise when it's boot but I stay with a white screen
- Press Option during startup: Display only a cursor, I can move it but I stay with a white screen
- Press N during startup: White screen with a hearth blicking
- Press T during startup: doesn't work (always a white screen)
- Press Shift during startup: doesn't work (always a white screen)
- Press Command-V during startup: doesn't work (always a white screen)
- Press Command-S during startup: doesn't work (always a white screen)
- Press Option-N during startup: doesn't work (always a white screen)

I guess is not a problem with the screen because I saw a cursor and a hearth.
Someone know how I can force to boot from the "Mac OS X Install Disk 1"??

Christophe