Client/Server doesn't work

[jacek]

class server : public QTcpServer, public QMainWindow

This isn't a good idea. Better use two classes --- one for the GUI and one for the communication.

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
server s;
...
server w;
...
}

Why do you create two servers and where's the client?