R7000 LAN ports only at 100M

> I was having issues with my router [...]

   Thanks for that detailed description.

> [...] Now my LAN is capped at 100M. [...]

   How did you reach that conclusion?  LED color?  Speed measurement?
Other?

   "capped" is not a useful problem description.  It does not say what
you did.  It does not say what happened when you did it.  As usual,
showing actual actions (commands) with their actual results (error
messages, LED indicators, ...) can be more helpful than vague
descriptions or interpretations.

> [...] I have the latest firmware [...]

   As always, an actual version number would be more useful than your
opinion of what's "latest" today.  And, on an R7000, its own opinion is
worth very little.

      https://community.netgear.com/t5/x/x/m-p/2069376#M186506

> [...] and my PC is updated. [...]

   Similarly uninformative, but any version of Windows should be about
as good as any other in this neighborhood.  What does Windows have to
say about the Ethernet interface on that system?

> [...] I'm not sure if it is my PC or the router. [...]

   Nor am I.  A bad Ethernet cable could explain this kind of problem,
too.

   Blame assignment is Job One.  Test/substitute things until you can
determine the culprit.

   For a quick cable test, connect each end to a LAN Ethernet port on
your router, and observe the relevant port-status LED indicators.  For a
good cable, both port-status LEDs should indicate a maximum-speed
connection.  (And they should agree.)  If a known-good cable does any
less, then I'd suspect the router hardware.

   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.