Hi

I am facing a problem that is "Database Connection error" on my blog since last two days I tried every thing but database is not connecting. My other sites on the same server are working well

Would you help me to resolve this Issue ??

I shall be thank full

Have you checked your WordPress config file to ensure it has the correct details of the database for the WordPress that is getting the connection error? This link will help you located the config file for your site - http://codex.wordpress.org/Editing_wp-config.php

Yes all ready check this. Configuration is right. I check this carefully

In Firefox it gives Connection Error when I open site in IE it show 500 Internal server Error

The internal server error is usually because of some error in the .htaccess file. Please try renaming the .htaccess file in both the root directory and wordpress directory to htaccess.txt.

Your .htaccess file (by default) should look something like -
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

The other reason of getting this error is when your php server is running out of memory if that happens the only thing to do is create a text file named php.ini and put the next line inside - memory=50mb

it does not work there is still DataBase Connection error please help

ask your hosting to check what is wrong,
quite possible that the forums DB was blocked, because of spam