500 – Internal server error after hit Login (WP-Admin)

Hello Friends,
I’m not been able to login my Admin Dashbaord page. Before 1 day its worked fine. After Entering (http://onlinemock.educationandcareer.org/wp-admin) login page appear and after click Login button show –

Site URL : http://onlinemock.educationandcareer.org
“500 – Internal server error.
There is a problem with the resource you are looking for, and it cannot be displayed.”

I am using –
– Plex 11.5 windows hosting
– WordPress 4.0

Web.config –

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.webServer>
        <rewrite>
            <rules>
            	<rule name="wordpress" patternSyntax="Wildcard">
					<match url="*"/>
					<conditions>
						<add input="{REQUEST_FILENAME}" matchType="IsFile" negate="true"/>
						<add input="{REQUEST_FILENAME}" matchType="IsDirectory" negate="true"/>
					</conditions>
					<action type="Rewrite" url="index.php"/>
				</rule>
                <rule name="WordPress Rule 1" stopProcessing="true">
                    <match url="^index\.php$" ignoreCase="false" />
                    <action type="None" />
                </rule>
                <rule name="WordPress Rule 2" stopProcessing="true">
                    <match url="^([_0-9a-zA-Z-]+/)?files/(.+)" ignoreCase="false" />
                    <action type="Rewrite" url="wp-includes/ms-files.php?file={R:2}" appendQueryString="false" />
                </rule>
                <rule name="WordPress Rule 3" stopProcessing="true">
                    <match url="^([_0-9a-zA-Z-]+/)?wp-admin$" ignoreCase="false" />
                    <action type="Redirect" url="{R:1}wp-admin/" redirectType="Permanent" />
                </rule>
                <rule name="WordPress Rule 4" stopProcessing="true">
                    <match url="^" ignoreCase="false" />
                    <conditions logicalGrouping="MatchAny">
                        <add input="{REQUEST_FILENAME}" matchType="IsFile" ignoreCase="false" />
                        <add input="{REQUEST_FILENAME}" matchType="IsDirectory" ignoreCase="false" />
                    </conditions>
                    <action type="None" />
                </rule>
                <rule name="WordPress Rule 5" stopProcessing="true">
                    <match url="^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*)" ignoreCase="false" />
                    <action type="Rewrite" url="{R:2}" />
                </rule>
                <rule name="WordPress Rule 6" stopProcessing="true">
                    <match url="^([_0-9a-zA-Z-]+/)?(.*\.php)$" ignoreCase="false" />
                    <action type="Rewrite" url="{R:2}" />
                </rule>
                <rule name="WordPress Rule 7" stopProcessing="true">
                    <match url="." ignoreCase="false" />
                    <action type="Rewrite" url="index.php" />
                </rule>
            </rules>
        </rewrite>
    </system.webServer>
</configuration>

.htaccess –

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

# STRONG HTACCESS PROTECTION</code>
<Files ~ "^.*\.([Hh][Tt][Aa])">
order allow,deny
deny from all
satisfy all
</Files>

# disable directory browsing
Options All -Indexes

# protect wp-config.php
<files wp-config.php>
Order deny,allow
Deny from all
</files>

# protect from sql injection
Options +FollowSymLinks
RewriteEngine On
RewriteCond %{QUERY_STRING} (\<|%3C).*script.*(\>|%3E) [NC,OR]
RewriteCond %{QUERY_STRING} GLOBALS(=|\[|\%[0-9A-Z]{0,2}) [OR]
RewriteCond %{QUERY_STRING} _REQUEST(=|\[|\%[0-9A-Z]{0,2})
RewriteRule ^(.*)$ index.php [F,L]

<FilesMatch "\\.(js|css|html|htm|php|xml)$">
SetOutputFilter DEFLATE
</FilesMatch>

<IfModule mod_gzip.c>
mod_gzip_on Yes
mod_gzip_dechunk Yes
mod_gzip_item_include file \.(html?|txt|css|js|php|pl)$
mod_gzip_item_include handler ^cgi-script$
mod_gzip_item_include mime ^text/.*
mod_gzip_item_include mime ^application/x-javascript.*
mod_gzip_item_exclude mime ^image/.*
mod_gzip_item_exclude rspheader ^Content-Encoding:.*gzip.*
</IfModule>

# Protect from spam bots
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_METHOD} POST
RewriteCond %{REQUEST_URI} .wp-comments-post\.php*
RewriteCond %{HTTP_REFERER} !.onlinemock.educationandcareer.org.* [OR]
RewriteCond %{HTTP_USER_AGENT} ^$
RewriteRule (.*) ^http://%{REMOTE_ADDR}/$ [R=301,L]
</IfModule>

My site is working fine. Pls help.