dropped internet after receiving alert pop up

Not exactly sure were to post this question so I'm posting here....

I had something weird happen this morning. I received a pop alert that someone had logged into one of my IP addresses (one I haven't assigned to anything) It was a quick pop up that disappeared. But immediately after that, my internet dropped, forcing me to reboot the modem & router. Fine, maybe a coincidence, but it immediately dropped again after coming back. This happened 2 more times. I called TWC and they pung me and told me to restart the router, and that seemed to work. At least it stayed connected while I was home. Could the two thing be related at all? Is there a log to show me who logged in? anyway to block them?

I just installed a (used) Airport Express the previous night. I assigned a name and a password, like I should.

Any ideas?

Thanks.