I don't know if this will help or not but with Mandrake the User Name & Password are [b]Case Sensitive[/b] which may be your current problem of why you can no longer get in.
As for the DSL not working did you install the Samba Package? If you didn't it's unlikely to work correctly and the other thing that you'll need to look at is how you configured the Network connections.
Add a comment about which version of Mandrake you have installed and I'll or someone else here will most likely be able to walk you through the process so you can get it working properly.
If you can not get into the OS I would just reinstall it to the same location and work from there with a new User Name & Password. You might find the following link interesting.
http://tinyurl.com/8b9s6
Col