> [...] Solid white light becomes solid amber on my router [...]
How many lights are there on your "my router"? _Which_ "Solid white light becomes solid amber on [your] router?
Visit http://netgear.com/support , put in your model number, and look for Documentation. Get the User Manual (at least). Read. Look for the LED descriptions. Now that we know what "amber" means, ...
> [...] when desktop computer enters sleep mode. [...]
On some computers/devices (such as your (unspecified) "desktop computer", apparently), an Ethernet interface will run at 100MHz when the device is in a standby or (not-truly) "off" mode. When such a device is awakened or powered on, it may negotiate a faster link rate.
If the computer's sleeping, then how important to you is the speed of its Ethernet interface?
> [...] Replaced Ethernet cable, [...]
If the cable was good when the computer was powered on, then I'd bet that it stayed good when the computer was shut down.
