Can't access Wan/Inet when modem plugged in

[kipsta]

WNDR3700 V2-DG834 V4 in Bridge Mode-1.5.4
Hi,
I have been running this setup for a long time and everything has been fine. As of two days ago though I can no longer access the inet or the router or modem (ping, browser etc).
If I disconnect the modem from the router and restart the router I can then access the router again. As soon as the modem is plugged back in and syncs the router seems to reboot and I lose all access again.
I have tested a combined modem/router and I can access the inet with no problems.
I have also tried a different modem connected to the router and I have the same issue.
I can access both the router and modem via the browser but as soon as the adsl connection sync's/login I lose access again

edit
oops Thanks for any suggestions

[kipsta]

Further information regarding the above issue.
It has been discovered that there is a comms cable fault between my modem and the exchange.
When a standalone modem/router is put in place, it is able to handle the fault and function normally.
When I use the Netgear WNDR3700 & the DG834 (in bridge mode) the fault seems to cause the router to continually reboot once sync is obtained.
I'm wondering if the initial fault corrupted the WNDR3700 and whether a factory reset might fix the problem.

Thanks
kip

[kipsta]

reset router to defaults. All's goof