TP-Link Archer C7 5Ghz network router and Dell Vostro 3550

I bought a TP-Link Archer C7 5Ghz network router and for a few days my Dell Vostro 3550 was able to see it.  My iPhone can still see it so it is still transmitting but my Vostro 3550 cannot see it although it can see the 2.4Ghz side of the router (dual band).
How do I get it back?
I am using Windows 7

Thanks