So here is what happend:

I wanted to install autodisconnect from extras-testing. Before that I removed the autodisconect script I am running for some months. So I moved the sh file from /etc/network/if-up.d/autodisconnect to somewhere else, then i killed the autodisconnect script.
Then I realized that my wlan won't connect anymore. So I thought I should reboot my device. When I pressed the power button the device was off immediately. When I press the power button now the LED and screen turn white as usual but stay on for about 10sec. after that the phone goes off again. I already removed the battery.

Damn, what have I done. root is not for everyone I guess

How can I get my N900 working again?
So many apps and data is on the device. Luckily I got a backup from PR1.2 update. Do I have to reflash?