Spin in the system backup you made before you started playing with this.
If you did not make a backup you just found out why you should have.
Now you may be looking at a bare metal install of w7 or a factory restore.
I have a Dell latitude e6400 running Windows 7. I love Windows 7. But I also like Windows 10. I found out I can have them both with a dual boot. So I todecided to try it. http://www.pcadvisor.co.uk/how-to/windows/how-dual-boot-windows-7-or-8-with-windows-10-3633084/ I used this, I didn't do the part With shrinking volume or whatever cuz I didn't no how. So I did the part with the BIOS so when I booted up my PC with the flash drive in it it booted to a MENU of options like install over Windows 7, and custom. I chose custom and chose the partition that had enough space (drive 0 partition 2) had 90 GB. Well Windows 10 installed and booted down. But when it booted back up it booted to the same menu I did it again not remembering what I did in bios was still active, so now I have 2 Windows 10 pro and 1 Windows 7 pro on the PC. I fixed what I did in BIOS and took the USB thumb drive out and now it says I wants me to restart to finish and I do it brings me to the windows 10 logo and says that again, if I hit the X it says I can go into either one of the windows 10 or Windows 7 but it won't load into any of them. I'm lost I don't no what I did wrong or how to fix it please help, also please help me firguing out how to uninstall one of the windows 10 installs, thank you in advance