Socket creation

Are you using winsock? If so, what is the error code you receive by calling the WSAGetLastError() function?

What might be a reason an application to be failing to create any sockets under windows 7 and in the same time to create them and run fine under windows xp?

Windows 7 has a stricter default firewall than Windows XP.

In general, when installing an application, you will want the installer to try to use the IpFwAdmin interface (or similar -- I forget what it's called these days) to allow your application to set up sockets appropriately.

This is assuming that you're already doing everything else right -- calling WSAStartup() with MAKEWORD(2,2) as the argument, using protocol values that are actually supported when calling ::socket(), etc.