Compatibility problem......between the driver and your motherboard or your display card or others! Check if the issue persists in clean boot state.

http://www.tp-link.com/Resources/document/TL-WPS510U_CompatibilityList_2.pdf

"Reason for doing this was that the adsl and internet lights went out intermitantly. The intermitant no adsl and internet has been ongoing for months." The problem maybe lies in your ISP phone line...

Have you tried to connect to the wireless network ? Any error message ?

Kane wrote The bridge of WR641G cannot support WPA ？ Yes， the WR641G cannot support WPA when it is in bridge mode.

Can the following link help ? http://www.tp-link.com/en/article/?id=411