Replaced Motherboard and Hard Drive

Good Evening, I have a Dell Inspiron 15r 5520 intel core i5 6GB Memory originally with a built in Microsoft Windows 8.

• Purchased in 2012
• It has since been updated to Windows 8.1 and Windows 10. 
• I upgraded to Windows 10 as soon as I found out Windows 10 was free for people who had Windows 8
• Windows 10 was working fine until July and then that's when the Motherboard 'gave out'
• I tested it and it said the Motherboard is fine it's just the HDD.

Well the Hard Drive and Motherboard overheated and both died.

• I have replaced a Heat Sink AND Fan to attempt to save it (Yes, I used a rice size amount of Thermal Paste to reinstall)
• So now I purchased a New 1TB (1000GB) 8MB Cache 5400RPM SATA 2.5" 9.5mm Notebook Hard Drive and that was fine.
• I also purchased a replacement Motherboard for my Laptop, which came with no Software, leading me to purchase Microsoft Windows 10 Pro.

• I have had trouble downloading the Windows 10 pro, as it would turn off during download and refuse to actually go on and give me the proper download for a while.
• After 2 days of trying, I finally realized I had to remove the CD once it was installed, and Windows 10 Pro was installed on my computer. After a few downloads, Skype, Google Hangouts and Roblox(Online game) to be exact, the motherboard fried out.
• I recently got a Motherboard on ebay from China and now I am trying a USA seller instead.

• Is Windows 10 Pro frying my Laptop? I know I cannot download devices from Dell any longer but I would at least like it to work.

Can I get the Windows 8 back for free? Can I call Microsoft and Verify my Old Motherboard's Information for a new installation? (I have my old items still and serial Number, I just no longer have a Warranty due to the time expiration.)

Should I upgrade the Memory and can my computer's Motherboard handle that?

A couple of notes with the new Motherboard:

1. My computer no longer had a Serial Number tied to Dell, but it was called a 'Inspiron 5520'
2. Windows 10 pro seemed to not work with the Motherboard.

Thanks for answering my questions, any help would be appreciated.