Hi
I've been running Sabayon linux for a long time and are very happy with it. Yesterday I installed Windows 10 on a extra (new) HD, went smooth.
When I boot, it would log me in to Windows 10 without providing me the option to select which OS I wanted to boot into.

So I run EasyBCD to alter my boot mbr menu.
I added a new entry (Linux), with grub2 selected.

When I reboot, I get the windows 10 boot menu which now shows two options (Windows and linux). After selecting Linux, the screen turns black and reads "Try hd(0,0): ext".

Can someone please help me out?
I've tried many things now, googled a lot - but I'm honestly stuck.

Thanks for any input.
Let me know if I need to provide any feedback/outputs etc.

Status quo: I can only boot into Windows 10 now. Thanks, MS

Had you googled prior to the install you would have found a LOT of advice about doing that the other way around, or not doing it at all.
Microsoft installs are well known for assuming that everything belongs to them and overwriting all other boot blocks without warning or recourse.

Ok, now that you are in the soup, know that there IS a way out. Google again, this time looking for how to recover the linux boot. You will find advice involving a live-cd version of linux (with a grub of the same major version as they one you have been using) and restoring (re-installing) the grub boot block install. This can be tricky, so read more than one and think about it a little first. You may want to boot the live-cd a couple of times and examine the detected devices and file systems before actually writing anything to disk.

Windows does not detect (or care about) linux or grub, but grub and linux can detect and play nice with Windows. Your grub should detect both linux and Windows and (once reinstalled) present a menu to start either you wish.

Remember this next time: the only safe order is windows first, then linux, because Linux can detect and protect Windows while Windows cannot detect or protect anything.

Pop back here if you run into problems.

M$oft just make things difficult - separate disks like that should be do-able.
At the blank screen immediately after power-on, get into the boot list (BIOS or UEFI should both have a key for this - watch the screen or try F12, F10, <Esc>, <Del> ...). Pick the disk that has Sabayon on it and boot that. If it's UEFI you may have to dig around to get the entry for Linux.
Once in Linux run these from a terminal (root/sudo as needed) and post the output

Hi again. Thanks for the replies, I've gotten much further now.
I was not able to boot into the linux disk, not even by changing the boot order in the bios (running legacy, non-uefi btw).
Looks like Windows 10 did a great job cleaning up all bootloaders

However, I did manage to re-install grub2.
What I did for this was:
- boot from sabayon dvd, recovery disk (made sure boot order was correct in bios)
- create dir /mnt/root
- OPTIONAL (if using LVM): had to run "vgscan" + "vgchange -ay MY_VG_NAME" first to activate the volume group
- OPTIONAL (if using LVM): run "sudo lvdisplay" to show logical volumes, and find the root volume
- mount /dev/MY_VG_NAME/root /mnt/root
- run "grub2-install /dev/sda --boot-directory=/mnt/root" (check that /dev/sda is your linux disk, could be sdb/sdc/... etc. as well)
- reboot, change boot order in bios (linux disk first), and reboot again

After this, I was booting into grub2 shell.

I am not sure how to configure my grub2 yet (so it shows "Linux" and "Windows 10"), working on that now.
Will post update if I figured it out.

Tip: if you have trouble booting into grub, create a bootable cd/dvd/usb with super-grub2-disk (http://www.supergrubdisk.org/super-grub2-disk/).
It can be quite useful.

Just run grub-mkconfig - presuming os-prober is installed (it generally is with grub2 these days).

Thanks again. This was indeed doing the job.
I had to boot into my linux installation first though, which I could only manage by using the "super-grub2-disk" bootable dvd.
When I did manage to boot into my linux installation, I ran:
- grub2-mkconfig

After rebooting and setting correct boot-order in the bios, the grub menu showed both linux (Sabayon) and windows 10.
Windows 10 works fine, but the linux entry fails to boot.
However, if I select "Sabayon recovery mode" and pick an older kernel, it works fine.

This however has to do with my linux installation and is outside the scope of this post (tips are welcome though ).

Thanks for the help!

you are using BACKWARDS Logic.

I have the same set up now too. one HDD Linux, the second HDD Windows 10

Grub uses it to boot. set your Linux to be the first boot HDD and let grub deal with it. so simple.
it will pick up windows done.