Need Help Grub Repair-Triple Boot Ubuntu,CentOs,Windows

Hello all,

I'm new to Linux. I had a ruing system with Ubuntu and Windows in MBR mode. Recently I converted the MBR partition to GPT using EASUS partition manager. Then I installed Centos 7 in UEFI mode , after which everything went kaput.

1. I used grub repair tool "boot-repair". But it didn't fix the problem. Instead it made the Quick Boot menu (F11) very confusing. I see 4 entries for the same hard disk.
I've three Hard Disks.
sda-->120 GB SSD
sda2-->Windows 10
sdb --> 2TB
sdc --> 500GB
sdc2-->Ubuntu
sdc5 --> Centos

boot-repair
http://paste.ubuntu.com/16020743/

2. Then I followed the steps mentioned on
http://askubuntu.com/questions/88384...alling-windows
But got stuck at grub-install /dev/sda (even tried with /dev/sdb and /dev/sdc/) where it says "grub-install: error: caot find efi directory"

3. Moreover I've 4 options for same Hard Disk in Quick Boot Menu. On entring these option I boot into:
a) Centos -->Centos Boot Menu where I have Ubuntu also. But if I enter Ubuntu, I get
can't find 'linux'
can't find 'initrd'
b) ubuntu --> grub Mode
c) Windows Boot Manager --> redirects to centos boot menu
d) SATA6 --> grub rescue Mode
Attached is the image.
Please see Centos option is working and I can boot into CentOs

4) I tried working from grub rescue mode, but ls command is not showing hd2 (sdc)

Can some please help me here. Thanks in advance.