What firmware version is loaded on the 4500 router? Is Rogers Cable or DSL? If you have v1.21, this could be the issue and was known to hang the router randomly. If so, update to v1.22 or v.23 is the latest. v1.22 fixed the random hang issue. Let us know if you need help updating.
Save off your config to file first, do a factory reset of the router, then do the update, do another factory rest, test if you want then reload the configuration file so you don't have to manually re-configure everything.