could you provide me your topology of network?

reboot the adapter and router. does the 5GHZ is work normal before you change the SSID and PSW?

are you sure the router is TL-WR543G? where is USB port? following is picture for the device: http://www.tplink.com/en/products/details/?categoryid=&model=TL-WR543G

you are lie. are you sure you use 340G?

when you plug it on PC, does the LED will flash?

can you install the driver by manually? click 'my computer ' on windows and select management->click device management -> chose the device on left screen and right click it-> choose update the...