Hi art123,
It sounds like the Cisco DPC3825 is functioning properly if you are able to get internet when plugged into it with an ethernet cable, we know at the very least internet signal is coming into the modem. When you try to connect wireless do you see other wireless networks that are around you? What is the name of your wireless network, and do you see it on the list? If you do not see any networks, it could be an issue with the wireless on the laptop being turned off or not functioning properly. You could also login to the router to verify that you have wireless enabled in the router settings so that it is broadcasting the network name allowing you to connect to it.