Question My entire HDD suddenly "Unallocated". I think I'm gonna pass out

Mar 5, 2019
My laptop is Lenovo Y700 17-ISK. It has internal 1TB storage and my M2 SSD where I have Windows. Today I changed my SSD to new bigger one. When I was installing Windows there were no problems. When there was prompt where to install Windows I chose carefully new empty SSD and didn't format anything. After installation and after going into Windows I noticed in "My computer" that it shows new SSD but no internal HDD. In "disk management" it shows as "Unallocated space". I provide screenshots of "disk management" view: View:

Can you please help if there is a way to recover it? I have many important files there. If someone could help me I am even willing to pay you. I am begging you :(
you might try reverting back to all original drives, and see if everything still works that way with original drive letters, boot order, etc...

If all works, move your stuff you need to an external USB drive...(then later, you can simply delete partition. format unclaimed space , etc., with no worries....

The current issue might be a thing with a new UEFI/Secure Boot installed OS refusing to recognize another OS previously installed in Secure Boot? Try AHCI mode over secure boot, and see if drive shows up...?