Media search not working

Based on what I’ve come across online and on this forum and after attempting practically everything that’s mentioned
here, here & here, my last resort was that confusing if statement…
if( !is_admin() ) add_filter('pre_get_posts','vibeExcludePages');
Where does this go? Which .php file to edit? I have to be doing something wrong!

For the sake of not getting ripped to shreds for not being clear, here are the details:
– Running WP 3.3.1, clean install w/ minimal plugins:
– Akismet (self explanatory and no issues I’ve found about that affect media search)
– cforms (form plugin, removed from WP repo due to something irrelevant here but also no issues noted)
– Google XML Sitemaps
– Hotfix (recommended in one of the previous links)
– WordPress Importer (data import tool)
All have been disabled and issue persisted… my logical deduction was that it’s the theme that’s causing this – just like the other posts.
I’m using a Parent/Child custom theme that, unfortunately, cannot be dropped as it has cost me in customization (design, coding…) and the headaches of having to deal with incompetence – reason why I’m here now!
Not to keep side tracking, I attempted to insert the code above in the functions.php (as I came to understand in one of the above posts) of the parent theme first, then the child theme and lastly, both of them at the same time… I put the code at the beginning of the files after the <?php tag. None had any effect, search was still returning 0 results despite there being well over 100)
So I’m at loss and I’m reposting this same issue – since the other posts had been closed for some time – I hope I’ve made my explanations clear enough and I truly hope there is an answer to this… seems ridiculous to go over tens of pages looking for a media element

Thanks for reading this and have a good one,
Fredo