Right-click the Start menu button and, from the list, click Command Prompt (admin) or Windows PowerShell (admin). You can also use the key combination <Windows> + <R> and type cmd in the dialog box and validate with Enter.
In the window that just opened, type the command sfc /scannow and press Enter.
SFC (System File Checker) is an easy to use tool directly included in Windows, so you don't have to download it. On the other hand, it is limited since it only checks system files, especially DLLs. If your problem is caused by a bad device driver or an error in the registry, it will unfortunately not be able to do anything for you.