Asterisk Freeze

We have a machine
Pentium III 700Mhz
Hard drive 120Gb
1Gb de RAM
running Linux Debian with Asterisk
Our application forward calls to destination and record them using mixmonitor ( all calls use G.711alaw).

After some days running well, the system hangs and we need to restart the machine.
Does anyone know what happen?
Is there any other information that I have to provide?

Some people have a problem when thier DNS stops working and asterisk cant do a look up for a specific SIP provider then it may hang.

If the problem is the DNS, is there a way to disable this feature?

Instead of having the phone register with the domain name try using the IP.