Cable internet does not work, but wireless and online games do?

I'm trying to help my mom solve an internet connection issue she's been having before she blames it on her actual PC. Her computer is connected by an Ethernet cable. On occassions usually twice a day morning and night she is unable to access the internet on her browsers (Fire Fox, IE.) Although online games that are started through an exe file work perfectly fine. At first I thought it was a virus blocking access to browsers but I found another Ethernet cable to try for myself. After a few hours my internet browsers stopped working too. One way we have found to fix the problem is restarting the modem by turning it off and on, it doesn't last very long though. Our internet provider is Wind Jammer Cable. My mom said they get a lot of complaints maybe they just suck I don't know.