you mean it can detect wifi networks but won't connect to any of them? Get any error msg? Maybe you can try some different drivers. Or maybe change the router's wifi channel

I think you can reset it one more time. maybe push the reset button 10~15 seconds until you see the all the lights blinking once. I know that because some people just push the reset 1 second and...

http://www.tp-link.com/en/faq-728.html?

Is the ADSL led light up? solid or flashing? since two modem routers have the same problem, it might be issue of ISP end as well

How about downloading the driver from TP-LINK website: http://www.tp-link.com/en/download/Archer-T8E.html#Driver? then install it manually: http://www.tp-link.com/en/faq-920.html

Actually the simultaneous clients number is also affected by the application of each client, for example, if they just browse the internet, there would be more clients connected, if they watch online...