sounds like your rewrite isn't working -> server config

what does that mean to a person such as myself, who is "code challenged" and new to elgg? Put more concisely, what is the solution? Thanks!

http://docs.elgg.org/wiki/Mod_rewrite_test

If rewrite passes then it's probably the same issue as above - you entered the wrong path in the installation script.  You'll need to find the datalist table and change the path make sure it has a trailing slash

Would the installation script change arbitrarily? I have had the site running for a week and the only thing I have added are a few plugins. It has been working fine. It seemed to do this just on its own. ?? sorry for the questions...how do I find the "datalist table" Do I just look in my file structure somewhere, or is it in the Mysql database somewhere" Thanks!!

Disable all your third party plugins. If you cant get to admin part of site, change the name of the start.php files in the plugins to start1.php for all your third party plugins. Then change back one by one and see which one is causing conflict

The better way of doing that is creating a folder called 'disabled' in the mod directory, you don't need to be messing with plugin files and you only have to create/delete it once.  It will keep the plugin activation status the same but won't actually load any of the plugins.  Then you can disable the few plugins you've added that way.

OK...thanks for both the suggestions. So, do I move one plugin at a time to and from the "disabled" folder until the problem goes away? I would have to do the way Matt suggested because I cannot reach any admin functions.

No, you just create a folder called "disabled" inside your root/mod directory. That will disable all plugins. Now try to login to the system.

Also check whether you are able to register, use the reset password options etc.. Dont forget to check for the existence of root/actions/login.php . May be you accidently deleted it?

OK...here's what i have done so far: I created a folder in the elgg/mod/disabled like you said, I have checked the elgg/actions/*.php files and "login" "register" and a couple others are there. My login screen went back to looking normal (before, it was elongated and vertically offset and other weird stuff) anyway, it still says "The action file for login was not found" in the little red banner. This is the way it looked in the beginning, when the problem first started, so there is progress...When I click on "Lost Password" it gives me this message:

"Fatal error: require_once() [function.require]: Failed opening required MYPATHWAYTOTHEFILESNOTMADEPUBLICHERE/elgg/pages/account/forgotten_password.php' (include_path='.:/usr/local/lib/php-5.2.17/lib/php') in MYPATHWAYTOTHEFILESNOTMADEPUBLICHERE/elgg/engine/lib/users.php on line 1141"

When I try to "Register," it gives me this:

"Fatal error: require_once() [function.require]: Failed opening required MYPATHWAYTOTHEFILESNOTMADEPUBLICHERE/elgg/pages/account/register.php' (include_path='.:/usr/local/lib/php-5.2.17/lib/php') in MYPATHWAYTOTHEFILESNOTMADEPUBLICHERE/elgg/engine/lib/users.php on line 1147"

I have obviously replaced the complete path with the statement "MYPATHWAYTOTHEFILESNOTMADEPUBLICHERE" for security.

I checked the views_simplecache under "data" folder and it had 22 files that look like ths one...013585ba60e3f2b35e1dfb33368a...in it. They were all created on the same day (3 days ago, the 10th) I'm guessing this is when the problem started. Does that have anything to do with this you think? I know it is just a cache, but would this point to any problem maybe?

Question: Could a person that registered as a new user, be able to disable the site somehow? I know this may be a little paranoid. but I know nothing about how to protect the site from this type of thing. 

Nothing to do with the cache - it's one of a few things:

1. MYPATHWAYTOTHEFILESNOTMADEPUBLICHERE is wrong
2. apache can't read the file
3. The file doesn't exist

No, a user can't disable the site.  At least there are no outstanding security flaws that I'm aware of, and if there were this doesn't seem like the likely outcome.