Thanks again Dave,
I was able to connect via SSH as well as by screen by this:
On the other hand for second problem I messed up with the configuration of iptables. The default gateway was supposed to be 192.168.1.1 but by mistake i save the script with 192.168.1.7 which wasn't allowing me to make my BB online and at the same time my connection get halted on my host os too.Thanks a lot for your time and help.