can't go http://localhost

i'm using dreamweaver mx and i'm building an asp page. each time i preview my page the address will go like this C:\Inetpub\wwwroot\mtomsystem\main.asp instead of http://localhost/mtomsystem/main.asp. when i open it manually with http://localhost/mtomsystem/main.asp address it cannot be open and show me this message:-

The page cannot be displayed
There is a problem with the page you are trying to reach and it cannot be displayed.
--------------------------------------------------------------------------------
Please try the following:
Open the localhost home page, and then look for links to the information you want.
Click the Refresh button, or try again later.
Click Search to look for information on the Internet.
You can also see a list of related sites.
HTTP 500 - Internal server error
Internet Explorer

Please anyone help me and teach me how to solve this problem. i'm fuzzy right now

regards
-osz-