Internet going down??

Every night the internet goes down I see all the workstations in logmein and then at around 930 pm there offline including servers.

In the morning the users come in reset the (Time warner is ISP T1 box ) power it back on and all is restored.

I have check the switch and firewall all is working am I right in say this is a ISP issue and they need to be told or do i need to check out some other things?

Thanks