Display not working and fan runs at maximum after HDD->SSD upgrade

When I turn on this machine, it boots up slowly but normally (with an external display). The internal display does not turn on at all, and during the startup sequence, the fan runs to maximum speed and stays there. The machine is useable for basic tasks (and the SSD is still faster than the old HDD), but anything CPU-intensive takes forever.

I checked my work after repairing and everything worked as expected at that point. The problems started after the computer was turned off and unplugged for about 36 hours.

I tried:

• SMC reset
• PRAM reset
• Connected to external display - the external display works but performance is slow; checked System Information and the internal display is not listed
• Downloaded TG Pro on recommendation from another forum to check temperature sensors. There is a temperature listed for the HD and display sensors (the HD sensor temp does not match the SSD’s self-reported temp), but diagnostics is not available in the free version - would it be worth it to buy a license?
• Ran diagnostics and got the following codes:
  • PFM006 related to the SMC (temperature sensors, according to other forums)
  • VFD001 related to the display

I have some ideas for what the problem might be that require opening up the computer again, but I’d obviously like to try anything that doesn’t require cutting the adhesive first.

• This model doesn’t need attention to the HD temperature sensor when replacing the drive, right? There’s also no separate connector for the display temperature sensor, but could either of those be the culprit?
• It’s possible that I got some alcohol inside the machine while cleaning the display adhesive. I think this is unlikely, though, because I cleaned off the frame in the upright position and anything would have dripped down towards the vents/speaker holes in the bottom. I tried to check that the display panel was dry before I put it in, and it did work for a while. Could corrosion cause both of these issues?
• The only other thing I can think of is if I didn’t seat the display data or power connector properly and it got loose. Would that cause the fan behavior, though?

Thoughts?