Hi iPhelex
My name is Andre Da Costa; an Independent Consultant, Windows Insider MVP and Windows & Devices for IT MVP. I'm here to help you with your problem.
If you do a reset or clean install, you will need to ensure your files are backed up and prepare to reinstall and potentially reactivate applications like Microsoft Office.
http://answers.microsoft.com/en-us/windows/wiki...
One way to speed up your computer is to perform a reset and choose the option to keep your files, you will need to reinstall your applications though.
Click Start > Settings (or press Windows key + i) > click Update & security
Click Recovery then click Get Started under Reset this PC
Since we are performing a clean install, I will be selecting the option Remove everything, if you don't want to do that, you can click Keep my files
Reset offers two types of clean installs:
Just remove my files - this option is quicker and recommended if you just want a fresh start and you plan to keep the computer.
Remove files and clean the drive - if you plan to giveaway or resell your computer, this option ensures the computer is cleaned properly. Its takes a bit longer, but it is recommended if you plan to no longer use this computer.
Since I will be using this computer, I will choose the first option.
Click Reset to begin
Windows 10 will restart
Preparing to perform a reset
Resetting - this might take some time depending on the amount of data
Windows will check the drive for errors and fix them.
Windows 10 performs a clean install again
Out of Box Experience (OOBE)
The Out of Box Experience assist with personlizing your Windows experience such as creating a user account, connect to a wireless network and adjust privacy settings.
Choose your country, language, keyboard layout and time zone then click Next
Read and accept the End User License Agreement
If you want to customize your privacy settings, you can do so now. Please note, you can always do this after setup (Start > Settings > Privacy). For now, lets use Use Express settings
Wait while Windows 10 restarts
Setup your username, password and a hint then click Next
There you have it, a clean installation of Windows
The alternative is to perform a repair upgrade: