All I can think of is uninstall and reinstall of the software, and pressing the reset button on the router - if it has got one - and see if the problem re-occurs. Check all of the physical connections - telephone line, DSL splitter, etc - and make sure that your PCI card is installed properly.
Do you still have the manuals?
Is the item still under warranty?
Does the manufacturer have a website with a troubleshooting section?
Hope this helps