This is probably because you installed Ubuntu in a different mode than Windows. If your device came pre-installed with Windows, I will assume it was installed using EFI mode, with fast startup enabled.
You will need to first make your Windows installation work (i.e. boot) again, then re-install Ubuntu using the same installation mode as Windows.
To do that, boot into your BIOS and change boot order, so "Windows Boot Loader" is the first. If you changed from EFI boot to legacy, change it back. If you disabled fast startup you may need to re-enable it (not necessarily, some installations will work regardless).
Once Windows is working, remove Ubuntu completely, by deleting the partition completely, and then remove grub from Windows boot loader.
When you are done with that, re-install Ubuntu using the same installation mode as Windows.
Note: you will need to use partition editing techniques and other methods that require some understanding and experience. Only follow the above suggestion if you know how to use these tools.