Boot failing on occasion, boots from drive that does not have OS

I have 3 drives. A 60GB Intel SSD which my OS is installed on, a Samsung 120GB SSD which has just games, and a 1TB HDD for all my other media and documents. A while back my power cut out and when trying to reboot it would fail until I tried booting from my 120GB SSD, which didn't make much sense as my OS is my 60GB Intel SSD. After that I had no issues for a long time until recently where my computer (after updating overnight is my guess) wasn't booting until I tried booting from my 1TB HDD, which confused me even more as again my OS is not installed on my HDD. And now I'm basically in a situation where my PC will boot every once in a while FROM the 1TB, today it wasn't booting from any drive for a while until I unplugged and replugged the SATA cables from all of them then tried again. Its a very confusing issue in my eyes, I have a backup of my OS on a hard drive and made a system repair disk for windows 10. I can give any additional information that I could possibly have if required, any help would be greatly appreciated, thank you.

Hello Civilian Welcome to the Ten Forums! And unfortunately as many have already seen the jumbles experienced with how the 10 installer works in contrast to what you have seen with previous versions of Windows. namely how 10 gets a little confused?

What happens with 10 where even when the OS drive is seen as Disk 0 in the Disk Management tool for example the 10 installer gets confused when other non OS drives are present while the upgrade or clean install takes place! The temp installation folders may end up on your 1tb drive for example while the boot files and mbr information goes to the 120gb SSD! Or vice versa seeing the temp folders there instead with the 1tb becoming the boot drive which is precisely the problem you are running into.

Now the two "Fast and Easy" solutions to correct this will require that you first unplug the 120gb SSD and the 1tb storage drive leaving only the 60gb SSD OS drive plugged in. Then you have the choice of the Reset PC recovery option to Refresh Windows 10 either by getting into the F8 boot options Advanced recovery tool section or by booting live either from the 10 media or even a Recovery Drive with an 8gb flash drive being another option seen now with 10 for creating recovery media with all the repair tools.

The other alternative option for getting things fixed before contemplating the last resort of seeing a full fresh clean install go on still only having the 60gn plugged in by itself would be the Upgrade to Repair Install method explained in the guide seen at: Repair Install Windows 10 with an In-place Upgrade - Windows 10 Forums

That will provide the option to keep all files and most programs during the OS repair which should see the boot sector rewritten for you. The last resort option however if you don't have anything much on the drive at the moment and can spare the time for a fresh install of 10 would don't see just a partial repair and find yourself possibly still stuck at Square #1 but go for broke with the full clean install to insure the working results! That means everything else has to go on fresh from scratch all over again however but will insure the boot issue is resolved where you can then replug the other drives back in but also check the boot order in the bios setup to see that the 60gb is set as the default HD usually at the top of the list of drives there.