struggling to boot back to windows 8.1 after installing windows 7

Hi. i need some help. i recently installed windows 7 ultimate on a new partition after having installed windows 8.1 pro. Now, after windows 7 is up and running, i cant find a way to boot back to windows 8.1. i checked msconfig and there is only windows 7 ultimate there and i checked under advanced settings in the system setting in control panel but it is not their either. i also tried using easybcd to check and create a new option that is linked to the drive where windows 8 is installed, but when i boot up and choose the windows 8.1 option, it gives me a 0xc0000428 error. can someone help please?

thanks

p.s my windows 8.1 drive was the C drive, but after i installed windows 7, that changed to the C drive and now my windows 8.1 drive is the D drive for some reason
My System SpecsSystem Spec

Usually dual-booting two [or more] Operating Systems requires a boot menu of some type at startup where the choice of OS to use is made.

Due to differences in the various versions of Windows it's frequently recommended to install the older version first.
https://www.google.com/search?site=&....0.R1igrBEdrWA

Are the C: and D: drives 2 actual drives or partitions on one drive?

As for the msconfig issue, Win8.1 can't show, the 2 OSes don't know about each other, that's a lot of what dual-booting is about. And yes, I have dual-booted in the past but find it much simpler to use a 4-port KVM and choose the version/computer I want to use, either WinVista, Win7, Win8.1 or Linux Mint 17.

Thanks for the help guys. I used my windows 7 installation disk I run startup recovery and it managed to recover both my windows 7 os and my windows 8.1 os so now when I startup I get to choose which one to start with. Thanks a lot guys.

That should have been configured when you installed 7 but it took extra repair to sort it.

Can we see a screenshot of Disk Management - Post a Screen Capture Image