my site dead on the exchange server ??!

Hi ,,

This my first time working with exchange server, installed and its works fine … but … today the web site not working befor was fine, and the strange the www.mysite.com/exchange works … but not www.mysite.com .. ping the site or the ip give nothing … what could be the problem ?

Win2003 server, exchange 5.2, with fix 5 ip ..

Thanks in advanced.