"internal server error" from wp-admin

Hi. Thanks in advance for help and consideration.

The site http://www.DallasEgrets.org/wordpress seems to be working fine.
However, when I enter http://www.DallasEgrets.org/wordpress/wp-admin.php, I get this error:

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, cgiadmin@yourhostingaccount.com and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.

This problem started when I tried to set the site so it could be reached via “DallasEgrets.org” without the /wordpress. I was able to do this for another site, though I have forgotten how I did it.
There is an older, non-wordpress site (quite ugly) at DallasEgrets.org that I am trying to replace with the snazzier wordpress version.

I am on shared hosting, so do not have access to server log.
wordpress is able to find the site templates and database, otherwise the site could not be rendered. I thought wp-admin.php would be in the same place.

I do not code in php, nor do I use mysql (except with the black-box wordpress front end) but I am willing to learn. I am comfortable working at command line and editing config files, but I can’t figure out what to edit.

Badly need help. Peak season for the egret society is about to start. Really need the dynamic management that wordpress supplies, can’t really manage the site manually anymore the way I did before. Thanks again.