Quirky Dahsboard Menu Tab

When I click on the Dashboard menu tab at the top of the admin area, I get a menu beneath which there is no content. The link it takes me to is:

[blog.com/wp-admin/admin.php?page=index.php]

It simply brings up a blank page beneath the menu options.

The link that the tab should direct to is:
[ blog.com/wp-admin/]
and works just fine.

I’ve tried a few solutions to this problem posted on the forums, with no luck. Most of them involve doing something to a /plugins/index.php file, either changing its name (from .php to .html, for example) or deleting it altogether.

When I do either, I get a simple message: “Cannot load index.php.”

I run several blogs, and in only one do I have this problem. It’s not such a huge deal since I know where the real dashboard lurks, but I’d like to repair the link properly for ease of use.

All that aside, though… There’s not a native […/plugin/index.php] file in the ordinary wp install. What gives? Why on earth would there be a redirect somewhere in the admin menus to this file?

Any thoughts on how to fix this are appreciated? Thanks!