My iMacs Display Screen Fell down I have an iMac (Intel 21.5" late 2013, 21.5 core i5). This morning, I replaced my hard disk with an SSD drive and used not a right adhesive tape to put the display screen back. At first, I was very happy as my iMac was much faster and even more quiet than before! After few hours of working with my iMac, the attack LED ( not the iMac) fell down from my desk on the floor.  I attached both display data cable and the display power cable, here are the symptoms:


The iMac LED it all black.
I connected the iMac to my external LCD monitors and it works fine, i can login and work with it fine
The Fan is constantly running. Why is that?
My iMac seems to be very slow compare to the incident. What could be the reason.


I suspect that either my mac’s display is damages or one or both of the two cables: display data cable and the display power cable are broken.

Any help and advice would be greatly appreciated.
You have two distinct problems with your iMac that you’re unfortunately conflating with the most obvious damage - the broken display.  


The display is most likely broken and will need to be replaced.  I can be tested, but not in a typical home or office environment.
The cable connectors on the logic board may be damaged as a fall like that will literally rip them off the board.  A visual inspection should be enough to verify if they are good or not
The fan spin is likely because you replaced your hard disk with a non-Apple one that doesn’t have a temp sensor.  A missing sensor will cause the fans to spin at full speed
The slow performance is likely due to the erroneous temp readings (from the missing sensor) and the Mac thermal throttling in response.


To fix the fan and speed issue, you simply need an inline temp sensor to send the correct data to the SMC.  However, the screen is quite expensive and you should get a quote on a replacement prior to doing this - it may be much more cost effective purchase a replacement iMac of the same vintage and sell that one for “parts.”

Also, if you’re going to replace a HDD and go through all the trouble on an iMac, you should spring for an SSD.  The performance gains are well worth it.