It's certainly not good that only power and LAN are lit up, means the modem has rebooted for some reason in most cases, and chances of them being able to actually access the modem IMO are slim... The following can cause a reboot.
Bad Coax cable - when the modem senses that the cable is potentially shorted, it will go into a reboot to see if it clears up, however, it can get stuck if the cable is actually bad. Saw this during the very first month that Gen4 was operational on a neighbors system.
Power Quality - the modem is connected to a known good outlet that is supplying between 110 and 125v with minimal noise, correct? It should not be plugged into a power strip, surge protector, nor an UPS. Most UPS used a modified sinewave, which can cause havok with the modem, and power strips can do funky things.
Bad connection of the cables, check to ensure the power cable is fully seated into the back of the modem, and at the wall. Never unplug power from the modem at the back, always unplug power from the wall before touching the connection on the back.
Faulty Modem - It happens from time to time, and a bad transmitter can also cause this issue, it will certainly require some good diagnostics from Liz/Amanda/Chris to see what needs to be done.
@Brandon - in my experience, if the System LED is turned off, you can't get to
http://192.168.0.1 Edit: Liz managed to beat me it looks like.. Bleh.