Win 10 is corrupt, SFC finds nothing, can't make boot USB

Out of the blue after a recent update Win 10 (64 bit Home on 7 year old Dell Inspiron laptop) is corrupt. The taskbar has lost all the pinned tasks; I can't add new tasks; left clicking on the Windows icon has no effect, pressing the Windows key has no effect, I can't type anything in the Cortana search field on the taskbar. Mercifully right-clicking on the Windows icon still brings up the long technical menu, and right clicking on the taskbar brings up the menu about cascading windows etc. I can't remember what simply clicking on the taskbar should do, but it does nothing.

So I ran sfc /scannow and it told me "all files are OK." So I thought I'd run it at boot time and tried to make a boot USB; but the windows media creation tool failed with error 0x80080005 - 0x90016. This doesn't seem a very helpful error, it's quite likely not related to the corruption and I don't want to get sucked into fixing unrelated errors.

What I want to do is to un-corrupt Windows / get the taskbar working again. What should I do, please?

Many thanks

Andy

You need to run a particular form of command if you're trying to run SFC from a command prompt outside windows (offline).

I'm puzzled 0- you said SFC /scannow passed. So why would you want to try to run it offline or again?

ISO: you can start here.
Download Windows 10 ISO File - Windows 10 Installation Upgrade Tutorials

Using the iso or a bootable medium you could do an in-place upgrade repair install which keeps almost everything.
(Boot normally, run setup.exe and follow through the prompts).
If unsure, there's a tutorial in the Tutorial section.