Can't connect to the Internet

[Hosam]

I have a strange problem with my MacBook
It can connect to my wireless router but it won't connect to the Internet
And once it is connected to the wireless router all other devices (my iPhone or iPad or my other laptop ) lose access to the internet!!!!
I don't know why this happens.
Previously I had Astrill VPN client to access the Internet with any restrictions from my country!! so once Astrill is running I have Internet access on my MacBook but none of the other devices can access the Internet!!
In order to fix this issue I had a fresh installation of snow leopard on my MacBook today because I thought astrill was causing this problem.
During the installation I was asked for my iTunes account and my Mac had access to the Internet to verify my account and pulled out my info. Once the installation was complete and I logged in to my MacBook with my username I could not connect to the Internet !!!!!
I don't know why! It is a fresh installation and I haven't installed any app on snow leopard !! So what could be the reason!!
Oh yes.. Once I tried to go online on my iPad i couldnt I had to turn off my MacBook and restart my modem to get Internet access on my iPad !,!,
Please help me out!!!!

 

[Detrius]

When you say it's a clean install, do you mean that you formatted the drive and did not restore your data from backup?