Did you try the Elgg Documentation site which has troubleshooting for this?

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

Yes. I was using Firefox, which resulted a blank page. I just used chrome, and it gets me a 404 page.

I even reinstalled elgg and created a whole new DB.

Also, just noticed that the 404 page is linking to
http://blah.com/action/systemsettings/install
& I only have this:
http://blah.com/actions/systemsettings/install

h-ttp://blah.com/action/systemsettings/install

h-ttp://blah.com/actions/systemsettings/install

If you'd read the troubleshooting doc I linked to, it will explain how to handle your mod_rewrite problem. You could reinstall a thousand times and it won't change anything until you correctly configure your server.

I've read through it several times.

Mod_Rewrite is enabled, and it works. and It's not the memory either, since the memory already is set to 64mb.

My last post on this: you have a mod_rewrite problem. You would not see a 404 error on /action/systemsettings/install otherwise because of the rewrite rule in .htaccess

RewriteRule ^action\/([A-Za-z\_\-\/]+)$ engine/handlers/action_handler.php?action=$1

Im sorry if it's frustrating for you to help.

In my .htaccess, I have the following 2 "action" lines, lines 209 & 211:

RewriteRule ^action\/([A-Za-z\_\-\/]+)$ engine/handlers/action_handler.php?action=$1
RewriteRule ^actions\/([A-Za-z\_\-\/]+)$ engine/handlers/action_handler.php?action=$1

I tried the mod_rewrite test that you posted earlier, and that worked, proving mod_rewrite was working.

I have the same problem - any hope for a fix

Upon completion of admin profile (could be any other user profile?)  seems that the default theme is working.  With this we can note that elgg needs at least one profile to work properly.

Also it is wise while working on elgg configuration to have "Use simple cache" turned OFF from Site Administration.