<p>After rebooting the Windows 2003 Server with the IIS I receive the follow error message:</p>

<blockquote>
  <p>Cannot connect to the configuration database</p>
</blockquote>

<p>in the browser. The error occur on different pages and with different clients. that I think it is a server problem.</p>

<p>What can I do to solve this error?</p>

A quick web search suggests that this error message is probably coming from SharePoint Services, and indicates that SharePoint cannot connect to its database.
There seem to be several reasons suggested:
The SQL database is not running, has been removed, or you otherwise can't connect to it (firewall, login credentials, network failure)
IIS is running in the wrong mode
The latter could be IIS 6.0 configured for IIS 5.0 compatibility mode, or the application pool configured for 32-bit worker processes on a 64-bit system.