Allright. So it took 14 posts in this thread to get to the point where I need to tell you this:

1.
The N900 is a great device but not made for people. The species it's made for is called nerds or geeks. The computer-type ones...

2.
Buying this machine as a non-techie will give you quite a nice phone out of the box, but that's it. After that point, you will have to start working yourself. See point 1.

3.
As a result of point 2, my machine is far from "the same machine as yours". I might have tweaked it, smashed it with a hammer to make it speak German (yes, it needs to be forced a litte to get it to do that) or whatever else has come up in that geek mind of mine (see point 1). So: Giving vague descriptions of symptoms of vaguely described problems is not going to help you. If you get an error message, post that error message without us having to ask for it.

4.
The mere fact that I asked for that information (see 3) should have been taken as a hint. To fire up google, or whatever it is that gets you going.

5.
The fact that you've been able to fill up your root partition means you've been man enough to take this phone beyond human userlevels. You've entered the geek zone. Now you need to be man enough to fix the problems you yourself created. Hint: Atilla has just mentioned one of those methods to start with a tabula rasa, a clean slate. Google his kindly offered proposal.

6.
You said you tried some commands that did not work. Make sure you use the right ones, so google, or use the search engine on this site.

7.
Last but not least. Your device is not a shitty machine! It is in the state it is in now because you chose the geek path, not the human path.