Did you follow the guide [guide|137597] using the special pizza cutter tool? Most of the time people damage the display just in the opening process. Often I encounter cut LCD cables where the tool used damaged them.
The act of replacing a drive in its self won’t affect the display only during the opening. SMC is dependent on access to the original HHD’s built-in thermal sensor, which is why one needs to install an external sensor as the third party SATA HDD or SSD don’t offer the needed output. Which is one possibility why the fan is racing and reviewing Activity Monitor kernal_task is running heavy, as SMC is creating unused threads to prevent the system from overheating which is part of CPU Safe Mode.