Which way of boot you are using? UEFI or Legacy？

UEFI!

Can you enter the EFI settings and check if the 'Windows boot manager' was at #1？

If so, adjust it to make deepin/uos the #1

If you cannot see deepin/uos and you are sure that you have already installed deepin correctly, well there is another plan to fix.

Boot the PC by an USB live and use boot-repair to fix. If that still didn't work ... I don't know any other solution.

Good luck for you

if you are using desktop PC, press del to enter setup, then set bootup sequence, slect the first boot device to be Deepin.

try this:

https://github.com/Inokinoki/QEFIEntryManager

Good Day!

I've installed Deepin in my son's computer and he is away with his mother! Today I got hold of him and we tried your solutions over skype. We set the boot to grub but the computer does not recognize it and boots windows instead. I've been installing and reinstalling Deepin over the years and this is the first time it's happened!

Next time my son's here with me, I'll download the iso from a different source and try again.

Thanks everybody for your advice!

Try function keys (Esc, F7, F8 F10, F12, Delete or some other) and choose your OS to boot.