There could be a couple of problems with this, and non of which are the ISP issue.
The first one could be a simple activation of the interface. You can try a shutdown of the interface and then a no shutdown and see if that works.
The next thing to do is make sure you have IP Routing enabled, it should be default depending on your IOS, but you may want to check.
Also check ip subnet zero and ip classless are enabled in the global config. Again these are items that should be enabled by default, but you may want to check.
If this does not help, put a PC on the ethernet side of the router and run a traceroute to see where the connection dies.
Remember, or better yet a word of caution, if you are running BGP it will take some time to establish the connection. The first thing to make sure of is the serial IP at the ISP end, make sure you can ping it. After that you will need to just run through the config line by line to make sure everything is turned on, and set up the way you want.
If this still does not help, let me know.
I may need to get a little deeper in what you have to help.
Also, don't forget to leave my consult fee at paypal?!?!?!
he he he lol!!!