pages do not open after permalink change. htaccess?

Hi there,
let me tell you the problem then hopefully you can help me figure out what’s the probem. Our webmaster is unavailable now but some pages of our website (thebeadtrails.com) do not open after we changed permalinks to default and than to Post name. Actually do not know if there was some custom structure previously but current version of .htaccess has the following code:

# Use PHP5.3 as default
AddHandler application/x-httpd-php54 .php

RewriteEngine on
RewriteCond %{HTTP_HOST} ^beadtrails\.com$ [OR]
RewriteCond %{HTTP_HOST} ^www\.beadtrails\.com$
RewriteRule ^/?$ “http\:\/\/www\.thebeadtrails\.com\/” [R=301,L]

RewriteCond %{HTTP_HOST} ^thebeadtrails.com$
RewriteRule ^/?$ “http\:\/\/www\.thebeadtrails\.com\/” [R=301,L]

RewriteCond %{REQUEST_URI} ^$
RewriteCond %{HTTP_HOST} ^beadtrails.com/400.shtml$
RewriteRule ^$ https://beadtrails.com/errorpage.shtml [L,R=301]

RewriteCond %{REQUEST_URI} ^$
RewriteCond %{HTTP_HOST} ^beadtrails.com/404.shtml$
RewriteRule ^$ https://beadtrails.com/errorpage.shtml [L,R=301]

RewriteCond %{REQUEST_URI} ^$
RewriteCond %{HTTP_HOST} ^beadtrails.com/Summerland%20Bead%20Trail/$
RewriteRule ^$ https://www.beadtrails.com/ [L,R=301]

ErrorDocument 404 /notfound.html

# 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

Is there any fast solution to fix the problem cus some important pages of the website do not load at all (without any 404 or other message, just a white screen)?

Thanks in advance. Much appreciated.