Usually it means that your hard drive has failed and that you need to replace it and reinstall windows on the PC.
However it could also be that the boot sector on the hard drive has become corrupted. Do you have windows 10 bootable pendrive. You can create one from MIcrosoft site by downloading the media creation tool, running thios tool will give you the possibility to create a bootable pendrive (on different PC). You will need this to reinstall windows 10 which will be automatically activated. Make sure to create the pendrive and install the same edition as you have installed on the PC which is no longer booting.
With the media creation tool you could also try to repair startup if the hard disk on the PC is still working. However usually it means that the hard drive has become defective.
Let me know if you need further help,
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