That's how USB sharing function on the router works... Why do you have to access it via Network Neighbourhood?

Run the utility for the powerline extender, login its web interface and check its wireless settings. Try the correct Wi-Fi name and password on Vita. http://www.tp-link.com/en/faq-398.html

Can you ping IP address of the router properly when it crashes or refuses to connect? Does it happen on all clients connected wired and wirelessly? Reset the router to factory defaults and...

http://www.tp-link.com/en/faq-923.html What's the firmware version of your C2?

Beta firmware released. Bug Fixes: DHCP server will be not working when setting DHCP Address Reservation which including specific characters for example a space in the Description box....

After firmware upgrade, did you reconfigure time settings? Provide screenshot of your configuration pls.