[SOLVED] wifi problems and beyond

[totenstrahl]

Hello.

I have one or several problems with my Xbian.

Main problem:
* Cannot connect to wifi.
Secondary problem: I do not understand how to
* edit files
* open a command line (I have a feeling the noobiness is strong with me!)

Background: I've recently bought a Raspberry Pi B+. (I connect via HDMI to a TV, have a 5V 2A power supply, wifi dongle, wireless keyboard.)
First, I installed the Raspbian OS and everything worked fine - in particular wifi access.

I realised that I wanted something like Xbian, and so I've now installed that instead (1.0 knockout). It works fine as far as I can tell, but I can no longer access the wifi.
I use
system > settings > xbian > wlan0 (with Type: DHCP )
and it finds my network in the scan. But after typing the password it just cannot connect (it goes back to the list of networks and when I close that box it says "Failed to connect to wlan0" ). Since all worked under the Raspbian OS I suspect there is some setting here that must be adjusted (rather than a hardware problem).

I've seen people having similar problems, e.g.
http://raspberrypi.stackexchange.com/questions/7872/wifi-connection-problems-with-multiple-xbmc-distributions
and suggestions include
* editing /etc/network/interface. I have no problem locating the file in the filesystem - but there seems to be no way to open it (despite clicking like a mad person). Is this because I somehow am a user without acces to these files? Is there no built-in editor in Xbian? I tried accessing the file from the SD card from my laptop, but it cannot recognise the file system (the laptop has Windows). I have not seen anyone with this problem which makes me think I'm missing something very obvious. (I thought this adress looked quite promising: http://www.xbian.org/getting-started/install-and-connect/#ssh but I get a "404 not found".
)
* connecting via the command line... I don't understand how to even open the command line!

Any help much appreciated!

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UPDATE :
This seems borderline silly, since I did not actually try this before posting, but a fresh install solved my problems. It now connects to the wifi without problems. Anyways, thanks to the people who gave suggestions - I got valuable info about how xbian is managed anyway.