Viber messenger not working on my ad-hoc wireless network
Because your friends iDevice works, it may make this consideration useless. http://www.viberfaq.com/why-cant-i-use-viber-on-some-wi-fi-networks/ suggests that these ports are required for Viber to work.


TCP: 5242 and 4244
UDP: 5243 and 7985 (9785) (7985 is the port specified on the Viber) troubleshooter


However, the symptoms of having closed ports would be no connection to Viber. Maybe there is an application taking these ports on your Windows Machine intermittently.