Hi, having a bit of trouble with my new Asterisk 2.7 installation,
Do i have to configure anything before a SIP extension will work?
I have built some SIP extensions as explained in many on line tutorials and I they’re OK
I have downloaded the X-lite 4 software but an unbale to get the xlite 4 account software to register with Asterisk 
Can anyone point me in the right direction? 
There isn’t an Asterisk 2.7. This is the wrong forum for support questions. I guess 2.7 is the version of something like FreePBX, so look for a forum that deals with that.
X-Lite is easy to configure for Asterisk, but we would details of how you configured everything, or protocol traces to work out what you are doing wrong.
Your right there isn’t 
i’m using the freepbx GUI
will have a look on some other forums