Can't get wireless connection on laptop using CM500

I installed this modem a few months back and have had no problems until I tried to get a wireless connection for my work Dell laptop. I can only use the internet if I plug it in. I can connect wirelessly at local restaurants. My cell phone connects wirelessly fine at the house. When I called Spectrum I was told because I bought my own modem I would have to contact the modem company. Can anyone help me?