Everything we do on a computer leaves some sort of temporary file behind. Browsers cache all of their content to speed up delivery of frequently used web pages. Often these temporary files can become corrupted by shutting down the computer with an application or browser is still open. Windows has a built-in cleaner called Disk Cleanup, but often it still leaves a lot of files behind, especially for some applications. CCleaner is Disk Cleanup on steroids.
The old standby of pressing F8 several times during boot to get a machine into safe mode is gone, well sort of. Yes, F8 does not work anymore but relax there is still a safe mode so you can find bad drivers, rouge programs and malware. When your system fails to boot forcibly shut it down by a long press on the power button. After two cycles of not booting your system should enter Windows RE(Recovery Environment).
The Windows upgrade had been a free upgrade for Windows 7 and 8 users until July 29th, 2016, at least for most people. Microsoft then started charging $119 for the Home Edition or $199 for the Pro Edition. For now, a backdoor has been left open, you can still get a no-cost upgrade to Windows 10. Read on and follow the link to a page for people who use assistive technologies.
You qualify for the free upgrade if you use assistive technologies. Assistive technologies, such as a magnifier to see the screen enlarged, a narrator to read the text in browsers or in a document aloud, keyboard shortcuts or an on-screen keyboard. Assistive technology provides additional accessibility to people who have physical or cognitive difficulties, impairments or disabilities.