MBP does not boot despite the chime and white screen

I try to fix a macbook pro A1278 2.4GHz. When starting it you can hear the chime, the screen gets white/grey. Nothing else happens. You have to push the start button for 5 seconds if you want to switch it off.

The keys do not cause any reaction. Except the start button.

What i have been trying until now:

• Several resets, pram and so on
• safe mode
• single mode
• verbose mode
• changed the ram
• changed the HDD Lion and Sow L
• target mode
• recovery mode
• dvd-boot
• aht-boot
• pushing trackpad-button to eject the dvd
• external keyboard / mouse

Nothing happens. But there is the chime and the bright screen. Has anybody got any idea? That would be great.