http://wiki.maemo.org/Updating_the_firmware

Good luck

The output is okay, there is no indication that something is weird or broken.
If a reboot does not fix things, you might try to get rid of the widgets and stuff on the desktops and apply one of the default themes to the desktop (if you had a custom setup, at all, this is). There is a chance that some misbehaving application is causing it.
Do you use a modified version of hildon-desktop, like the CSSU (community seamless software update) version or MAG's modified hildon-desktop?

JonWW, do I only flash the rootfs, or do I need to flash the emmc aswell? Furher can I download some of the programs that I had from a website since I don't have a wireless connection for my n900 for the next 3 weeks, or is there a way to connect my n900 to my laptop and use the laptops internet access?

Michaaa62, I have rebooted it several times, everytime I reboot, it start up ... the welcome tune sound very scratchy, the it goes to the desktop, with black background and then it start throwing all this error messages like ... 'unable to perform operation, internal error' and 'application mail closed, internal error' and 'application web closed, internal error' etc. It repeat that lines over and over, without me doing or opening anything. I've closed all widgets changes themes etc ... nothing! Further I can't change the background, it stays black.

I always flash both, if you have everything backed up then I would do both.

You can try USB networking, http://wiki.maemo.org/N900_USB_networking I have not tried this as I have Wifi so cannot verify how easy it is to do.

You could try an adhoc connection to your laptop's Wifi
http://talk.maemo.org/showthread.php?t=5816
http://www.brighthub.com/computing/w...cles/7785.aspx
http://talk.maemo.org/showthread.php?t=40617

Hi Michaaa62

My phone decided it doesn't wanna boot anymore. I only get the white screen and then it goes dark and then after few seconds white again. Took out battery several times, rebooted, plugged into usb, plugged into charger ... orange light doesn't even go on.
I haven't flashed it yet, because my internet connection isn't too fast and further I can't download 190mb of data ... for the reflash. Are there anything else I can do?

If not a reflash, then may be Customer Care is your last hope?
Sounds that the hardware is broken not the software, i am afraid.