Computer unresponsive after aborted Windows 10 upgrade

My mum started up her computer one day and it came up with the message 'upgrading to Windows 10'. I am unsure if she accidentally selected this without realising it or if Windows forced the upgrade but as she didn't want it she clicked 'decline' once the installation had completed and was then told the computer would reinstall the previous operating system (she is unsure of the actual wording of this message).

The Windows 8 menu came up but is completely unresponsive. Upon turning on the computer she is able to log in as normal and it goes through into the Windows menu but is unable to access anything, with either the mouse or the touchscreen. None of the apps will open, she cannot get to the desktop, the menu will not swipe through.

I tried some keyboard shortcuts and the only one I can get to work is ctrl+alt+del which will go through to the option to lock, switch user, sign out or go to the task manager. I click on task manager but it just takes me back through to the windows menu which again is completely unresponsive. You are able to shut the computer down from the ctrl+alt+del page but nothing else. I have also tried using ctrl+shift+esc to get up the task manager which was completely unresponsive but when I pressed the windows key the windows menu flicked off for a second and I was able to see that the task manager is open but I cannot access it. The only thing it stated to be running was Skype but I was unable to click onto more details to see what else is going on in the background as it disappears as soon as it appears.

I tried to boot up safe mode by pressing F8 as it was loading up from being turned off but this did nothing.

Any help on how to either make Windows 8 operational or complete the aborted Windows 10 upgrade would be greatly appreciated. The computer is completely unusable in its current state.