|You have a wireless router not a modem FYI|
I would suspect its the pcs power management that is the issue. Its a known issue that when the network interface setting is for windows managed windows shuts the nic down. Most times it takes a reboot to get it back live again.
Go to the nics properties via lan connections and then to the power tab. Disable power management on the wired and wireless nics.
Answers are only as good as the information you provide.
How to properly post a question:
Sorry no tech support via PM's