How to fix blackscreen Bootcamp after SSD install

Question

Hello
I have an iMac mid 2011 21,5". I decided to boost it a little and that's when my issues started. Got no big problem to remove the optical drive, replace it with an SSD & add few gigs of RAM, but when I started to install windows 8.1 pro with bootcamp on the SSD, and keep the old HDD with MAC OSX I faced big issues.... (basically black screen with underscore blinking top left)
I read here, especially from Loner T, that it was expected, as Bootcamp was installing something in the NVram to tell the iMac to read the CD in SATA rather than in USB. I tried an EFI installation, but that was a bad idea, some devices were missing (sound card, classical) and there was some BSOD that made no sense
So I read that one option would be to modify the plist file, and add the USB boot, and try to install Windows that way, but rather than doing that option that I found a bit unreasonable (I guess that if USB boot is disabled for bootcamp for mid2011, there's a reason...?) ; I launched Bootcamp from Mac OSx, downloaded the utils/drivers on the USB key, selected the SSD as target harddrive and when the iMac rebooted I shut it down, replaced back the optidrive instead of the SSD, and put the SSD instead of the old HDD. Fans were running loud/full speed as expected as the old HDD was not here with its thermal sensor, but at least, when I restarted, Windows 8.1 pro installation started, and went till completion without an issue.
I stopped everything, removed again the optidrive, and then but back the old hdd (for Fan issue + space matter) and put back the SSD at Optidrive space.
and then rebooted... and faced something unexpected.
At boot, I have again the blackscreen with underscore blinking...
If I press ALT at boot, I can choose Mac OSX that boots well and properly. But if I select my SSD with Windows detected, I have the black screen.
I wonder if everything is lost, or if it's just something to repair in the boot sequence...
I have to admit that this is way above my skills
if someone can help me, I made some sudo commands in yosemite, to share here and eventually find a solution...
diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                  Apple_HFS Mac OS X                59.6 GB    disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk1
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *128.0 GB   disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:       Microsoft Basic Data BOOTCAMP                127.8 GB   disk1s2
diskutil cs list No CoreStorage logical volume groups found
sudo gpt -vv -r show /dev/disk0 gpt show: /dev/disk0: mediasize=500107862016; sectorsize=512; blocks=976773168 gpt show: /dev/disk0: PMBR at sector 0 gpt show: /dev/disk0: Pri GPT at sector 1 gpt show: /dev/disk0: Sec GPT at sector 976773167
      start       size index  contents
          0          1 PMBR
          1          1         Pri GPT header
          2         32         Pri GPT table
         34          6       
         40     409600 1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
     409640  116448792 2  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
  116858432    1269536 3  GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC
  118127968  858645167       
  976773135         32         Sec GPT table
  976773167          1         Sec GPT header
sudo gpt -vv -r show /dev/disk1 gpt show: /dev/disk1: mediasize=128035676160; sectorsize=512; blocks=250069680 gpt show: /dev/disk1: Suspicious MBR at sector 0 gpt show: /dev/disk1: Pri GPT at sector 1 gpt show: /dev/disk1: Sec GPT at sector 250069679
      start       size index  contents
          0          1         MBR
          1          1         Pri GPT header
          2         32         Pri GPT table
         34          6       
         40     409600 1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
     409640       2008       
     411648  249657344 2  GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
  250068992        655       
  250069647         32         Sec GPT table
  250069679          1         Sec GPT header
sudo fdisk /dev/disk0
Disk: /dev/disk0              geometry: 60801/255/63 [976773168 sectors]
Signature: 0xAA55
Starting       Ending
#: id  cyl  hd sec -  cyl  hd sec [ start -       size]
1: EE 1023 254  63 - 1023 254  63 [ 1 -  976773167] <Unknown ID>
2: 00    0 0   0 -    0 0   0 [         0 -          0] unused    
3: 00    0 0   0 -    0 0   0 [         0 -          0] unused    
4: 00    0 0   0 -    0 0   0 [         0 -          0] unused    
sudo fdisk /dev/disk1
Disk: /dev/disk1              geometry: 15566/255/63 [250069680 sectors]
Signature: 0xAA55
Starting       Ending
#: id  cyl  hd sec -  cyl  hd sec [ start -       size]
1: EE 1023 254  63 - 1023 254  63 [ 1 -     409639] <Unknown ID>
*2: 07   25 159   7 - 1023 254  63 [ 411648 -  249657344] HPFS/QNX/AUX
3: 00    0 0   0 -    0 0   0 [         0 -          0] unused    
4: 00    0 0   0 -    0 0   0 [         0 -          0] unused 
Thanks in advance !

Answer 1

Can you boot Windows from SSD when it is in the Main drive bay?
According to iMac (21.5-inch, Mid 2011) - Technical Specifications, there is an option to
Storage1
2.5 GHz
500GB (7200 rpm) hard drive
2.7 GHz
1TB (7200 rpm) hard drive
Configurable to 2TB hard drive or 256GB solid-state second drive, only at the Apple Online Store.
Can you check if your iMac has a second SATA port in the main Bay?
Please see https://www.ifixit.com/Guide/Installing+iMac+Intel+21.5-Inch+EMC+2428+Dual+Hard+ Drive+Kit/6434 for details.