i can't connect to the network why ?

Your question is very open and unspecific and therefore is hard to answer accurately. Did you really want an answer? It is hard to answer without knowing what software you use.

Or was your question an attempt to somehow criticize gnutella, because sometimes you cannot connect to the network instantly.

The gnutella network is transient. That means some parts are not always available to you. I have used both Bearshare and Gnucleus to connect to gnutella. You just have to be patient, read up the web pages and your clients help files.

When you download Bearshare it has a little application that checks the status of your computers connection to the net, have you tried running this?