router has started dropping connections to computer

My computers (Pentium IV with Intel motherboards and Ethernet ports)
connect to the Internet through an SMC7004VBR router fed by a SURFboard
SB4100 modem connected to Comcast's cable. My connection had been very
reliable until last Wednesday. Comcast admits they had service problems
most of that Wednesday. Since then my router often drops the connection
between my computers and the router. The connection between the modem
and the server may also be dead, but I have no way to tell.

Normally, when I connect a port on the router to a computer using an
Ethernet cable, the corresponding "power" light on the modem turns on.
When the connection between my computer and my modem drops off, that
power light goes off. Soon after it starts flashing, and typically the
connection is re-established within a few minutes. I can expedite the
process by running "IPconfig" from the RUN in the WinXP pro window.

I do know the problem is not an intermittent power connection to the
router because the router clock does not reset to midnight as would be
the case with a power failure.

I suspect the problem is somehow linked to Comcast, but I can't see how
something coming down the cable could break the connection between my
computers and the router. The router is set up such that only machines
with specific MAC addresses are supposed to be granted LAN access.
Access to the router's control panel requires a password.

Ideas on the cause of the problem would be welcomed.

WindsurferLA