Solved W7 unbootable after installing 8.1, need urgent help

My PC specs: Asus P8Z77-V with a SATA2 WD Caviar Black 500GB. The HDD has three partitions, and I've had Windows 7 32 bit installed on C:/ for three years.
Before installation, the BIOS has Secure Boot and CSM enabled.
Yesterday, I cut D: into two partitions, and use the second to install Windows 8.1 64-bit through a DVD. The installation went perfectly fine, and the new OS works wonder. The partitions now look like this (all primary, C is active):
C:/Windows 7 <> D:/Stuffs <> E:/Windows 8 <> F:/Stuffs
However, whenever I try to boot into Windows 7, I always receive an Windows Boot Manager error of "0xc000000f A required device isn't connected or can't be accessed".
- First thing I done was popping in a W7 repair disc, however no problems were reported.
- Then I disabled fast startup in W8, however it still uses the hiberfi.sys file.
- I started msconfig in W8, and choose W7 as the default OS. Nothing changed.
- Disabled Secure Boot and enable CSM to support both UEFI & Legacy in BIOS. Nothing changed.
- Aligned partitions and rebuilt MBR in partition wizards. Nothing changed.
I give up. I have tried every option possible. The only fix options I found left was winload.exe, bcdedit or using easybcd. I'm going to give it a shot but can't guarantee how will it turn out. Should anyone help me with this specific problem, I'd be greatly appreciated. Thanks for reading.

My guess would be, and this is strictly a guess, the x64 install overwrote the 32 bit boot manager used for Windows 7.

You have a Legacy install, and if you keep the 32 bit version of Windows 7, it will have to remain a Legacy install, so the CSM needs to be enabled.

Ah, thanks for the reply, but I fixed it awhile ago. Turned out simply replacing winload~1.exe with winload.exe did help.
The old winload.exe doesn't have a digital signature, which I think have been mentioned on this forum ago. Still thanks, I was panic at the thought of having reinstall Win 7 all over again