Windows won't boot anymore (c000021a)

Thanks for your reply John
Nope safe mode blue-screens as well

thanks Andre

You should get the Hardware test application from you computer manufacturer, make a bootable USB for the tools and test hardware.  

Then, if hardware is OK, you need to back up and reinstall Windows.

Check your hardware (cpu, disk, memory)  to make sure it passes basic diagnostics.   You don't describe the PC, so its hard to say which self booting tools to use (some boot to DOS, Some Linux, some will not work with UEFI).  Newer PCs pretty much are all setup to boot UEFI.   Some allow you to change that in the bios config, so do not.  

Lazesoft suite has a stable of tools to help repair Windows start up issues.   Download it to a good PC, it will allow you to create a bootable USB or DVD/CD.   The latest version gives an option to create a UEFI bootable or Legacy bootable device -- select wisely.  Then you can try those tools on the failing PC.   It boots into a windows environment, so you have some of those capabilities (like windows explorer) available as well.   It does NOT include hardware diagnostics, but if it boots up, that's an indication CPU and memory might be OK.  

If you create a bootable USB, you can add a few diagnostics on the USB.  Just add a Tools folder to the USB that Lazesoft created, then place any windows portable apps like memtest and cpu stability test or others in that folder.   Later, when booted from the lazesoft disk, you can access those simple tests and run them.

See:  http://www.lazesoft.com/lazesoft-recovery-suite-free.html

See: https://www.portablefreeware.com/index.php?sc=217
for some portable testing apps.  Note, some have a  64 bit and a 32 bit version and require the matching version for your PC

This client has chosen to have the computer reinstalled without any further investigation of the cause for its breakdown

Thanks for the update