Fusion Drive upgrade to SSD problem

I have a late 2013 21.5 iMac and using 1TB Fusion drive option.

I want to swap the HDD to SSD lately and I did some research so I planned to do below

1. Clone everything by Carbon Copy Cloner
2. Remove boot camp.
3. reboot to recovery mode. open terminal, split fusion drive
(Step here: https://www.lifewire.com/split-fusion-drive-apart-2260166)
4. shut down. open the iMac. swap the drive.
5. boot the iMac using USB drive (from step 1, tested) and clone everything back to internal SSD.

I have done all the step to 5. No matter how I boot up my mac, the screen is black. It has the start up sound. mouse and keyboard have light on.

I tried:
Cmd-R
Cmd-opt-R
Cmd-opt-P-R
Opt

I triple check the display connection to make sure they are connected as well.

HELP! Any hint or any alternative step are very welcome. Thanks

 

Hey. Thanks. I checked all the visible connection again and they are all connected as expected.
Do you think it would help if I swap the old HHD? Or you think it is other hardware failure?

 

so the grey screen with apple is there with or without any disk
seems i hv complete f___ up

 

thanks. I tried reset PRAM. no luck. (it does restart again after a while)
sadly i do not have any thunderbolt VGA/DVI converter and do not have any external mon (iMac and MBA only). I am thinking to borrow.
If external monitor shows up, then we can conclude that it is the display connector that I probably break?

 

I have just used it to split fusion drive so I dont think monitor or logic board is broken. mostly likely is the display connector but it looks alright to be.

Anyway I booked genius bar on Sunday to see why. Thanks all.