Hi

EPiServer CMS 5 has a new url (custom) for admin and edit mode. Try going to the front page, right click, and choose either edit or admin mode from the menu.

Windows admins always has right to enter admin and edit mode.

Try to login as an windows admin user and make sure EPiServer is using Windows login, which you find in web.config.

Then try to right click on the front page as Fredrik Vig suggested, you should then get a window which you select editmode.

If this leads to an incorrect link, then youre site configuration may be corrupt. Check the virtual path Util in web.config as well as all references to  edit and admin. Make sure they are correct.

There is also a phenomena whereby the user publishes his Visual Studio project, but certain EPiServer inception files do not get carried across.  This causes strange behaviour.  The 404 error appears but confuses most users because of it's custom nature.   It pays to have an existing site of the same (or as near as possible) so that you can copy the IIS settings (or export if using Windows Server 2003).  It's the kind of cutting-your-teeth task that comes with the terrritory on EPiServer it seems!