So I'm really out of ideas when it comes to this, but let me try to explain the situation really quick and simple.
I have a laptop, running Win 7 Pro x64 on a mSATA SSD 60GB drive (let's call it drive A). The other hard disk on my laptop is a 1TB hybrid (drive B). Both are formatted with NTFS file system, although it seems that the OS drive is with MBR and the hybrid is GPT (what these really are, I'm not sure). Finally, I have another spare 60GB 2.5" SSD drive (let's call this one C) that works and is just not used. I can connect it, however, through an USB adapter. The laptop itself is a Lenovo ThinkPad Edge E530 and as far as I know, supports both UEFI and the old legacy mode. Right now I'm using legacy, because of Win 7. After purchase, it came with Win 8 preloaded, but I uninstalled that and went for Win 7 instead.
I want to have the system dual-boot ready, so that I can run both Win 7 and Win 10 while keeping the same drives connected (or connect the spare C and somehow boot from there through USB). I got Windows 10 from the official media builder or whatever it was called and so I burned it onto a DVD. So this is all the stuff that I have right now.
What I have tried so far is:
1) install Win 10, from the DVD, onto the separate SSD drive C. Windows cannot install through connected USB adapter so I had to take the PC apart, unplug hybrid drive B and then put drive C into that place. it installs and works fine when I change the boot order. problem is that I still need my hybrid drive..
2) so I restored the original configuration, with drives A and B in their places, and with drive C now out again, with Windows 10 installed on it. but if I could not install when the C drive was out, I could not boot from it either (using the USB adapter). it says boot manager is missing or something.. I tried some solutions, which promised to put the necessary boot files on the drive. didn't work..
3) so finally, after trying many things, most of which I've already forgotten (there was a program called Rufus at some point, though..) I created a new partition on drive B, 250GB size, and thought 'yes, this will work!'. booted again, from the DVD and the installation is launched and then it tells me I cannot install Windows 10 on the hybrid drive, because it is a 'GPT drive' or whatever.
After about a week trying to make it work, I'm losing hope, really. Can it be this hard? I just want to have my current working environment accessible as well as the new Windows 10. I need this so that I can set up everything correctly in the new Windows, while still being able to work in Win 7. Once the setting up period is over and I'm happy with it, I want to buy 2 brand new SSDs, one mSATA and the other 2,5" SATA and then migrate the new, preconfigured working environment of Windows 10 onto the mSATA and keep the other one for programs.
Please, what do I need to do in order to make this happen?