Check to see if Comcast is reporting an outage for your area (see https://www.xfinity.com/support/cable-tv/outages-in-your-area/).
If no outage is reported and you want to troubleshoot this yourself, please see Connection Troubleshooting Tips. If you still need help, please provide Information Requested for Connection-Related Posts.
It's best to use an Ethernet cable connection if possible while checking the reliability of your connection to Comcast.
If you can't find the problem or you'd rather have Comcast do the troubleshooting, call them at the phone number on your bill or 1-800-Comcast, or chat with them using one of the "Trouble" options at https://www.comcastsupport.com/chatentry/. If they can't fix the problem remotely, insist they send a tech out to identify the cause and correct it.
If the tech finds bad coax, splitters, amplifiers, or connections in your home (even if Comcast originally supplied them) you'll probably have to pay for the visit unless you have or sign up for their Service Protection Plan (https://www.xfinity.com/support/account/service-protection-plan/, about $6/mo) and keep it for at least 60 days. If the trouble is due to a faulty Comcast modem, eMTA, gateway device, or anything outside your home, you shouldn't be charged.
Hello Worrywalrus, I do show that we are doing some work on a local node in your area that is directly impacting your services at this time. We hope to have the problem resolved within the next 72 hours, for updates please download the "My Account" app or go online to www.comcast.com.
Hi Worrywalrus, I wanted to check back in with you to see if you're still experiencing issues with your modem connecting to the internet. I show that everything should be repaired on my end, if you need assistance please reach back out to me here.