Get an external USB drive, copy everything to that. EVERYTHING, you are done. When you dump the old computer, take out the hard drives and put them in a safe place. You might never need them, but if you do, that's the back-up of the backup.

If your experience with WIN10 was an upgrade, that's the problem. A new computer that hasn't been 7,8,vista or something else, will work fine. Upgrade has traditionally been a failure. Upgrades are nothing but trouble for drivers and old registry entries and just make for a failure waiting to happen.