that's the most common reason for service interruption on USB modems, but I'm an ADSL user so can't comment on cable connections.
Best advice I can give is to google around for your isp and for your modem to see if there are any known problems.
It could be their servers having trouble. This is the case for my isp who still have large scale downtime and problem areas because of the blast virus. My isp has a homepage where it tells you the current status of their servers and the connection, and dailup and broadband both have orange light status (red fully down, orange problems, green all good
)