How to fix blackscreen Bootcamp after SSD install

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 !