OK. You decided to install the Windows 10 Technical Preview on a secondary machine. Just because the OS is going to change and you should expect hiccups and problems.
So, lifeHacker put together a nice guide. You can find it here: http://lifehacker.com/windows-10-technical-preview-now-available-for-download-1641212531
Also, please read Island Dog's post in this section today. You can find it here: https://forums.wincustomize.com/458063/page/1/#3497085
If you need help in backing up a disk (and doing it sector by sector with verification) and have no program to do it: http://www.ghacks.net/2014/08/08/best-free-drive-backup-programs-for-windows/
And read the instructions first!
Good luck and have fun!