If the downstream and upstream lights go solid for a bit before going back to blinking at the same time then it is locking successfully, but it's not liking something in the configuration it's getting.
Pull up the web interface »192.168.100.1
and go to the 'Configuration' tab and click the 'Reset All Defaults' button. That button does not reboot it, so after waiting a few seconds either power cycle it or click the 'Restart Cable Modem' button.
If doing that doesn't fix it, please post the info from the 'Status' 'Signal' and 'Log' tabs.