Dual boot Windows 10 and Windows 7 not working

I am having a ISO file of Windows 10 TP. I am already using Windows 7 in my pc. I want to test Windows 10. So it is good to create a dual boot system. I do not want to remove Windows 7. I created a 30GB partition for that. After installing Windows 10 when I restart my pc, Windows 7 is gone. I cannot see any dual boot menu on boot. I can see the system turning on directly in Windows 10. I want my old OS back as it is having lot of data on the desktop. It would be pain to re-install everything back again from scratch.

Data backup is not complicated. But here the boot loader is gone due to which you are facing issue. You have to use a live disc to backup the data first. Then go with any kind of troubleshooting. Or else you will loose your data. There are ample of live cd that you can use. Create a bootable disc and then boot your system with that. Copy the files and then go ahead with troubleshooting. I think you have to run a repair setup back with windows. The repair setup will not remove the data on your system.

This is due to messed up bootloader. And it can be fixed. Always install the new OS after. First you have to add Windows 7 and then you can go ahead installing Windows 10 so that the new bootloader can provide you dual boot menu. Here you have to use Windows 7 bootable disc. Just insert the disc and boot your system with that. And from there you have to choose Repair. Select Startup Repair from the menu. It will scan your pc and fix the bootloader. Then reboot your pc and you might get dual boot menu on your system.