Internet lights constantly blinking.

Modem lights keep continuously blinking. I called comcast and they kept sending signals which did not help. This has been going on for over a week now. I have unplugged the modem many times to no avail. The tech on the phone said not to worry about the lights that the modem is active. Now for the last several days, I have intermittent speeds on web sites and I keep getting no connection for no reason at all causing me to reconnect and re try the lost web site. I think that I need a new modem. This one is wireless and about 20 months old and a rental from Comcast. Any help?