Connection Troubleshooting Tips - an additional tip
Very good too bad you turned off replies because you forgot one thing.
When you have checked everything else and your still stumped take a look at the A/C Adapter AKA Wall Wart, power supply. The SMC modem has a pretty good A/C adapter, the Netgear does not, but this advice applies to ALL NETWORK GEAR THAT USES AN EXTERNAL POWER ADAPTER
The Netgear modem uses the standard A/C adapter that Netgear ships with just about all of it's consumer gear. It consistes of mostly empty air and a small circuit board containing a switching power supply. This is the same kind of power supply used in a computer. It has been years since any manufacturers used wall warts that consist of transformers+regulators. They have all gone to these mini-switchers because it saves weight and lowers their shipping costs.
The older transformer A/C adapters quite often lasted for many years. In particular ones that output A/C power like 9v A/C are known to last practically forever. You can for example purchase old electrical devices from the 1930's that use the exact same type of transformer internally and still work. These devices have taken millions of spikes over their lifetimes without any trouble.
The newer switching power supplies can fail rapidly. They are very suceptible to overvoltage conditions and powerline spikes. Many I have cut open to see why they failed have failed due to Electrolytic Capacitor Bulging and Splitting Open which is a known problem that has dogged the electronics industry for many years. In a few cases I resoldered in a new electrolytic cap and the supply went back on the device which then stopped having problems!
Unfortunately many times the failure is merely that the supply cannot maintain voltage under load. So the tech suspects the power adapter, unplugs it to test, puts a voltmeter on it, it measures 5 volts, and he figures it's working. But when plugged back into the device and load is applied the output voltage can drop. The CPUs in network devices have a very narrow tolerance for voltage drops and will not run reliably much below 4.85v or above 5.15v What is even more frustrating is sometimes unplugging failing supply from one device and plugging it into another device that uses less power, the wall wart will manage to keep voltage up under the reduced load and everything will continue to work. So it looks like it's working when it was tested with another device.
Worst of all is an internal electrolytic capacitor failure in these wall warts because the supply will still supply 5v even under load but there will be a strong 60Hz ripple that cannot be seen without an oscilloscope, yet can cause intermittent failures and unreliability in the device.
I have lost track of the times I've picked up smallish 4 port gigabit switches from the $5 bargain bins at Goodwill and plugged them into a good power adapter and they work fine. Many are now at critical places at customer sites of mine and are working fine - or will work fine until the new wall wart I put on them fails. Who throws away/donates to Goodwill a 5 port gigabit switch? Nobody except for the person who thinks it has "gone bad"
Anyway, the moral here is this: Manufacturers use external "wall wart" A/C adapters because they don't have to then U/L list the device, and because the Chinese make these things on assembly lines running a million miles a second. THEY ARE GARBAGE made with the cheapest parts imaginable. And manufacturers are stuck buying them because a better external adapter wall wart isn't manufactured in quantity since the race to the bottom on these has priced decent ones out of the consumer market. So, if your having intermittent problems, DO NOT rule out a power supply failure just because the power LED is on!