I have been searching someone else having the same issue but I couldn't find any. Here is my problem:

I'm using Windows 8 Pro with Media Center. File search screen does not close itself after I make a file search within start screen. It stuck on that screen. I can't go back to desktop, therefore, task manager is inaccessible. Only way to get out of it is to sign out. It also looks like non-operational. It doesn't give me any result at all. It's just a blank screen with "Files" title. It used to work perfectly. 

Things I have done before coming here:

1. Safe mode minimal boot to ensure no other 3rd party software interferes.
2. sfc haven't found any inconsistencies.
3. Search index has been rebuild.
4. Normal boot with all 3rd party services and start-up items disabled.
5. System restore to a date that I know this feature was functional.

And by the way, I have installed all updates released so far.

I strongly used file search via start menu back in Windows 7. This is an absolute game changer for me. I'm curious what causes this. I'll do a "system refresh" if I can't fix this. I'm working on it, I'll keep this thread updated should I find any fix.

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**First update:**
I just discovered that file search screen gets stuck if it's invoked by typing query directly in start screen. It doesn't get stuck if it's invoked from win + x menu. I was able to "escape" from stuck screen with invoking it again by win + x menu. After rebuilding search index again, search suggestions started to appear again but still there is no file search functionality.

**Second update:**
"Results for" expression appears only for a second near to "Files" title when search is initialized.

**Third update:**
As a last resort, I finally tried to do a "System Refresh" which has also failed to refresh by giving an error after waiting almost 20 minutes at 99%. (Seriously?) After cold boot it began to undo changes. After changes were reverted, I boot the machine without doing anything further and bingo! Search began acting normal again. This is a totally weird solution. It obviously fixed certain system files during failed refresh, and kept those changes untouched because they were supposed to be that way at the first place. I'll keep this thread alive should anyone comes with a more logical explanation. 

**Forth update:**
After a windows update, search functionality **again** stopped responding. It happened after a system update for the first time. Now I have a pretty good suspicion about system update, though I have no solid proof of its involvement with this problem.