You can kill the Cortana app from the task manager and try using search again. This issue was discovered on very first build and Microsoft has not patched this bug yet.
How to Fix Windows 10 Search
- Go to Control panel and change view by to large or small icon.
- Select Indexing option.
- Choose advanced settings.
- Now choose troubleshoot and search option.
- Choose first option to fix search issue on your Windows 10.
The troubleshooter will find and fix all issues, but if this method doesn't worked then you can try killing Cortana from tast manager.