asterisk users - Nov 2005 - FXO module picks up but incoming callers only hear the ringing tone.

My problem is that the Asterisk CLI reports that the caller has been 
connected to the voice menu (IVR) system, but the caller does not hear 
the menu. They only hear the ringing tone/toots/beeps. It seems like the 
module is damaged because replacing the FXO module with a new one fixes 
everything.

I've had this problem happen 5 times already, each time on different 
modules. Hence, different ports on the 4 port Digium TDM board. The only 
way I've fixed it is to replace the FXO module with a new one. If I swap 
a failed module into a working slot, it still failes leading me to 
confirm that it's the FXO module that's bad. Sometimes (but not all the 
time), when a module exhibits these symptoms, I can't call out through 
that module either.

Anyone else experienced this problem before? If so, can it be fixed in 
software? Or maybe a way to 'reset' the module? I'm beginning to
wonder
if it's my PC hardware that's causing the FXO modules to fail.

My setup
Dell Dimension 3.0GHz machine
512MB RAM
80GB hard drive
(think that's all the relevant PC data)
3 x 4 port Digium TDM cards.
- 2 cards with 4 FXO modules
- 1 card  with 4 FXS modules (never had problems with these)
- 4 SIP phones.

Thanks for any help/advice.