US led flashing is due to return signal cannot send back to cable company or cable loss larger then standard.
Typically is 32 dB ( count from splitter leg outled to modem signal inlet ) and 42 dB found very unstable. Try using a first outlet to connect the cable modem will get a better result. If online successful, check all cable connections and make sure all connections is good . If still offline may be the amplifier fault outside , better call the cable guy to find out what is going wrong.