Here's how a typical set-up would look like in our homes. Please take some time to locate (A), (B) and (C) before moving on to the troubleshooting steps below.
B: Broadband Termination Unit (BTU)
C: Residential Gateway (RG)
Below would be the steps for troubleshooting:
Turn OFF the power of (A), (B) and (C). After 10-15 seconds, turn the power back ON.
Wait for the Power and Internet LED lights on (C) to turn green and stable.
Are you having slow speed on a Wireless (Wi-Fi) or Ethernet connection?