I'm having an issue with my speed being limited to 100mbps dispite my adapter being 

I have already:

• set the adapter to auto-negotiate speed
• established that the connection can be faster than 100mbps (direct ethernet cable to the router gives 800)
• checked for needed driver updates
• obtained new ethernet cables (that give 800mbps when plugged directly in)

I think the issue might be because my router offers a 2.4 and 5g Ethernet - and only the 2.4 is making it through the adapter (as far as I can see) any ideas how I could change that?

Thanks in advance for any help.