Can't call outside numbers

Hi. I’m new to the Asterisk.
I’m configured two TDM400P cards. and everything was working until today.
I have 6 pstn lines with 6 different phone numbers. When i try to call out it calls only trough one line. If 3 callers trying to call out one of them getting busy tones so his calls don’t go through. Can any body help me to find my configuration mistake?
Thank you!