I needed to free up some disk space and according to tutorial DietUbuntu (https://help.ubuntu.com/community/Diet%20Ubuntu) I removed following packages:

ppp pppconfig pppoeconf wvdial
Since then my wifi and ethernet connections doesnt work. Installing those packages on system didnt help.

Here are outputs of some commands:

martin@compal:~$ sudo ifconfig 
lo        Link encap:Local Loopback  
          inet addr:  Mask:
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:39565 errors:0 dropped:0 overruns:0 frame:0
          TX packets:39565 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:1156417 (1.1 MB)  TX bytes:1156417 (1.1 MB)
martin@compal:~$ cat /etc/network/interfaces 
auto lo
iface lo inet loopback
martin@compal:~$ ping www.google.com
ping: unknown host www.google.com
What should I do?
Thank you!