No internet access

My wifi has been saying its connected with no internet access for at least a week now. I have a wifi extender downstairs since my modem is upstairs, and the network created from the extender has full access, but my regular wifi has no internet access. I've done all the troubleshooting and restarted the gateway multiple times and nothing works. It may be ok for a few minutes after a restart but then goes back to no internet access. My modem is 5 years old. Could it need updated? I work from home and need full internet access