Hey there, yesterday I installed Deepin and it completely wrecked my GRUB menu. Up until then I had Windows 10 installed in one partition and Bunsenlabs on the other without any issue. I installed Deepin on the Bunsen partition and choose to install GRUB on /dev/sda, and now I don't have any grub whatsoever so I'm stuck in a bootloop.

Unfortunately Deepin doesn't have a live CD, and I don't have a second computer in order to flash something like Grub Repair or another distro, so my question is if it's possible to do something from within Deepin's install command line (which I can access through Ctrl+alt+f). Also the installation doesn't give out much info so I'm not exactly sure why is it failing.

Thanks!

add this to /etc/default/grub
and comment out any lines with hidden in them and run update-grub

There is no file like that, but I do have a /etc/default/grub.d folder with some cfgs on it. Not sure if I should make a file with that name. Also I don't have the update-grub command.

Post the contents of /boot/grub/grub.cfg if it exist.

It doesn't, the only thing on it is a folder called themes.

Miss-read your first post. General directions on how to fix:
mount the deepin partition at /mnt
mkdir /mnt/boot/efi if it doesn't exist
mount the efi partition at /mnt/boot/efi
mount --bind /dev /proc /sys /run to /mnt/dev /mnt/proc /mnt/sys /mnt/run
chroot into /mnt
grub-install /dev/sda
update-grub
exit
unmount everything reboot
There are several how-to instructions on the web that give detail instructions on how
to re-install grub by chrooting into the system

It matters how you installed Deepin. Most Win10 installations are done in UEFI mode. When this is true, Linux needs to be installed in UEFI mode as well. Is that what you did? If you did, directing Grub to /dev/sda was a big mistake. We can only guess what you did, and guessing usually isn't very helpful. Output from fdisk -l or parted -l would help. If either show you have an ESP partition, then the best way forward will probably be to start over installing Deepin, but this time ensuring its installer boots in UEFI mode. There are usually two ways to do that. 1-go into UEFI BIOS setup and disable legacy booting. Legacy booting may be labeled CSM. Booting only in UEFI mode per BIOS setup will ensure Deepin won't boot in legacy mode. The other way is to use your BBS hotkey during POST to bring up the BIOS' own boot menu, where you should be able to select booting Deepin in either UEFI mode or in legacy/CSM mode, and would need UEFI, unless Windows is not installed in UEFI mode.

Having a Legacy install of Deepin with an EFI install of windows will require you to access the BIOS firmware on boot to change systems. Grub legacy will not boot an EFI install of windows on the same drive.

The fact that you have no /etc/default/grub or grub.cfg file would indicate that the install of Grub was not successful so I would agree that the first steps to take are suggested above, post the output of fdisk -l or parted -l and mount the efi partition and post its contents by following the commands suggested in post 6 above. All these require root (sudo) permissions.

You may need to reinstall in EFI mode as suggested if you have no entry for Deepin in the efi partition.

No, Windows is not installed in UEFI mode, I should of have said that. Everything is on MBR mode. Also I don't see anything regarding these modes at installation, it didn't make me chose. Maybe it's installing on UEFI mode instead of MBR? How could I know that?

The part about mounting the efi partition can be skipped.
When grub-install is run it will display the mode. To force grub to install in mode different of boot mode:
for bios mode or use x86_64-efi for uefi mode. If booted in bios and install grub in uefi mode will get a no nvram error and wont' have a boot option in the uefi firmware/bios bootloader, however if have the option to boot from file in firmware/bios will allow to boot in uefi mode.

Here's fdisk output: https://ibb.co/9GDzhrx

I have no grub-install nor update-grub commands. What I do have is grub-editnv, file, ftest, glue-efi, kbdcomp, macbless, menulst2cfg, mk*.*, mount, probe, render-label, script-check and syslinux2cfg.

If you have not chroot into the system you won't have any of these commands.
based on our fdisk output:
reboot, if don't have grub-install run before running grub-install

Went through the steps and everything seem to go ok, it found both the Deepin and Windows partition and it gave no errors. However after rebooting my PC still doesn't find any where to boot. I went into the bios just to make sure I'm using CSM and I am. Changed it to UEFI just to see what the happens but it's the same.

Also for what is worth I found I can boot into a Deepin desktop by just removing a parameter on the USB boot menu, so maybe that could make things easier? I'm not sure what to try though.