Why does a Windows 10 Pro computer not run any programs due to suddenly missing .DLL files?

So the computer at the business I work for has suddenly been unable to launch any programs. They all give the xxxx.DLL is missing error, usually the file VERSION.DLL.

I’m unable to update or restore as the windows update launcher is affected so that’s no good. Windows defender is also unresponsive so I can’t check for viruses. I cannot restore as the pc has no backup images. It has lost basically all functions bar; settings, file explorer and control panel. It has been plagued with issues the past few weeks, boot looping, file explorer crashing repeatedly etc.

The system is an Intel Core 2 Duo, 4GB RAM 120GB SSD running Windows 10 Pro.