Problem with Cortana and other things :/

Hey all, I've had this problem since I've upgraded my Dell Inspiron 11 3000 laptop from Windows 8 to Windows 10. After bootup, sometimes my Cortana Search Bar will stop working (though I don't get the typical Cortana and start menu critical error). After this other problems seem to follow, such as Youtube randomly freezing and becoming unavailable, Skype cutting out and saying there is a problem with my recording device, and whenever I try to open a photo or video on my computer I get an error message saying the wait operation timed out. Also, my screen brightness will become locked at its current setting, as when I press the two keys to turn it up/down they do nothing. I have the latest updates for Windows 10 and the latest drivers for my machine as of writing. I hope there's somebody who can help; if you need any information I'll try my best to inform you. Thanks. :)

Thanks JohnC, I'll give that a try and let you know what becomes of it.

JohnC;
I followed your instructions and ran the sfc/scannow command. It didn't fix anything, so I followed the advice on the page you provided and ran the SFC three additional times with Fast Startup turned off and restarting the computer after each time. I tried the Dism/Online/Cleanup-Image/RestoreHealth command, but it found no corruption. I restarted and tried the sfc/scannow again, but no avail. I continued down the list of potential fixes until the only one remaining was to refresh Windows 10. I successfully refreshed and things were running smoothly, until one of my programs (Avast antivirus) prompted me to restart my computer for updates. I did so, and it took a while to restart until eventually giving me a message at the bottom saying "Preparing automatic repair", and "Diagnosing your PC". It eventually took me to a screen where it said "Your PC did not start correctly" and gave me several options. All of the options either brought be back to the failed restart screen or did not work. I eventually had to reset my PC to factory settings and load up Windows 8.1. Things are running fine at the moment.

Will do, thanks.