Reinstall/Format Windows 7 on a multiboot system

Hello.
I have a Windows 7 on C: and Windows 8.1 on D:

A few weeks ago I received Black Screen of dead with mouse cursor (No Task Manager/Safe mode) in Windows 7, so now i want to get format drive C and do a clean install.
Should I just format drive C:? will i be able to boot windows 8?

Here's a screenshot of Disk Management. I know it's a mess.

If you're sure that D is large enough for your Win7 needs, then yes you can just format it during booted Clean Reinstall
Windows 7.

If not then I'd move the data off of F, during install use the Drive Options pictures in steps 11/12 of Clean Install Windows 7 to delete both D and F, then create a New Win7 partition of the size you want, followed by a new F partition in the remaining space. Format both partitions, be sure to choose only D to begin install.

This should configure a Dual Boot with Windows 8. If not install EasyBCD (click Download - no Name or Email required) to add Windows 8 to a boot menu.

Hi greg.
Thank you for your reply.
I did format C and installed Windows 7, but now Windows 8 is gone. Haven't tried EasyBSD yet, I will let you know about that.

Was Windows 8 there before you reinstalled 7? Did you not touch its partition during reinstall? If not then it will still be there and needs only to be added using EasyBCD as I've already explained.

If that fails then you can run Windows 8 Automatic Repair
to start Windows 8 and add Windows 7 if it doesn't do it for you.

Yes. Windows 8 was there.l've Added Windows 8 using EasyBSD. But when I boot Windows 8 it says "Windows cannot verify signature driver" and says sth about wiinload.exe. So I can't run Automatic repair.
1) How can I fix this?
2) How can I restore graphical bootloader now that I have no access to Windows 8.

Run Automatic Repair from the Windows 8 disk System Recovery Options - Boot to in Windows 8