My computer all of a sudden won't boot from a certain drive.

monicatiptop

Commendable
Oct 20, 2016
30
0
1,530
So yesterday I installed a new HDD and ram. The computer was booting perfectly fine and I turned it on and off multiple times. Then all of a sudden after I went out, the computer stayed on the startup screen (the computer didn't crash or do anything funky btw). I eventually changed the boot HDD to the new one and now it's working, but I'm confused as to why this happened? Also, by the way, I still have all my stuff on my old HDD, the majority of it is still working and it's still connected to the computer (and working), it just for some reason didn't boot from it.
That brings me to my next question, is there a particular way that I can make some of my old programs that don't seem to be working work (I know this is a very broad question, so if there's no answer that's fine)?
My specs are: AMD Phenom x4 925, GTX 1050ti, 8gb ram, 1tb HDD (new HDD, currently what is the boot drive), 500gb HDD (old HDD).
Also sorry if this is confusing, it's just that this problem is new to me.
 
Solution
you stil have a os on the old hdd and does the new one is plug in the first sata port on bard and made as first boot device in bios .

monicatiptop

Commendable
Oct 20, 2016
30
0
1,530

but why didn't it boot wth the old HDD?