Pleaze problem with registering to asterisk

i’m using asterisk1.2.7.1 and i configure sip.conf right to accept user with username=mus and password=mus but when i try to login to asterisk server through xlite it dosn’t work it keep trying to login and donna find the server .
it is just like if u donna have sip server at all
so would u plz help me 2 solve this prob??

This can becaused by multiple issues. Sounds like the computer that xlite is on can not connect to asterisk. Did you ping it ? Also please post your sip.conf