Assuming you have a 500 Error or "Internal Server Error" after you have just installed Word Press and have gone to your Admin to login here is the easy to follow fix.
Go to your admin directory commonly labeled "WP-ADMIN" open it up. Now you want to create a file called "php.ini" . Inside this file you want to put the single line
" memory_limit = 32M ; " without the quotes .
You can actually do this on your local computer in notepad and upload it or you can do it LIVE in your cPanel or favorite FTP program if it allows you to create and edit a file.
Simple as that. Now go login..