tmollai, you issue is probably not related, you should open a new thread. before you do that, you should do what they will tell you to do anyway, de-activate all of your plugins and see if you can post. Then re-activate one at a time, until you isolate the one that is causing you issues. Then it would be best to open a thread on that plugins support page.
opendoorsgallery, make sure you opened header.php in your theme or child theme folder. The whole code block looks like:
<script type="text/javascript">
jQuery(document).ready(function($) {
$.supersized({
slideshow : 1,
autoplay : true,
start_slide : 1,
random : ,
slide_interval : 3000,
transition : 1,
transition_speed : 500,
new_window : true,
pause_hover : ,
stop_loop : ,
keyboard_nav : true,
performance : 1,
image_protect : ,
image_path : 'https://www.opendoorsgallery.com/wp-content/plugins/wp-supersized/img/',
min_width : 0,
min_height : 0,
vertical_center : true,
horizontal_center : true,
fit_always : ,
fit_portrait : true,
fit_landscape : true,
thumbnail_navigation : ,
thumb_links : true,
slide_counter : true,
slide_captions : true,
slides : [
{image : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/odstartslide.jpg', title : ' ', thumb : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/thumbs/thumbs_odstartslide.jpg', url : ''},
{image : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/submitslide.jpg', title : ' ', thumb : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/thumbs/thumbs_submitslide.jpg', url : ''},
{image : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/Homepage-CE.jpg', title : ' ', thumb : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/thumbs/thumbs_Homepage-CE.jpg', url : ''},
{image : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/charreada-slide.jpg', title : ' ', thumb : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/thumbs/thumbs_charreada-slide.jpg', url : ''},
{image : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/Homepage-NS.jpg', title : ' ', thumb : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/thumbs/thumbs_Homepage-NS.jpg', url : ''},
{image : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/keepingbees.jpg', title : ' ', thumb : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/thumbs/thumbs_keepingbees.jpg', url : ''},
{image : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/journal-slide.jpg', title : ' ', thumb : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/thumbs/thumbs_journal-slide.jpg', url : ''},
{image : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/impression-slide.jpg', title : ' ', thumb : 'https://www.opendoorsgallery.com/wp-content/gallery/slider/thumbs/thumbs_impression-slide.jpg', url : ''}
],
slide_links : 'blank',
progress_bar : true,
mouse_scrub :
});
});
</script>
You can see the random parameter a few lines down from the top. If this code block is not there, then this code is being built in someplace else. If the slider came with your theme, contact the theme authors if possible and explain the issue. They may be able to help.