South Bridge error on thinkpad

This is a long story but essentially..

After reading here and some other places that replacing the current screen on my T450 laptop (1600x900) with a 1080p screen was possible I decided to give it a shot.

I went to a repair shop near to me and they said that while it was theoretically possible to do they wouldnt be comfortable sourcing a screen themselves. I subsequently got them a screen (from a legitamite supplier) and they agreed to try and upgrade it. They tried to upgrade it and it didnt work saying it was for another laptop (t440s or t450s). All well and good. So they put the old screen into my laptop and gave it back to me but I found out that the second battery in my laptop wasn't been drained. Everything else worked fine. I took it back to them and they repaired it after a week (after initially saying there was nothing wrong with it). It turned out to be a short circuit and they had to replace a fuse. That was fine. Anyway when I got the laptop back the joystick wasn't working, nor was the 3 mouse buttons at the top of the touchpad..so I took it back.

So today I got the laptop back and..they still werent working. The manager explained to me that the computer had, what he believed was, a "Southbridge error" and that as so much time had gone into the laptop he wouldnt fix it for free. Also because I had sourced my own screen, he wouldnt replace the damaged laptop.

My issue is... the laptops joystick and 3 buttons were working perfectly before I brought it in over the battery issue, not the screen issue, so to say that a southbrdge error caused by the screen was the cause of the problem strikes me as extremely suspect. Does anyone have any experience with this kind of incident. If it was caused by the screen company I'd hold them responsible as they specifically said that the screen was an upgrade.. but as it was a delayed problem that only surfaced following the battery replacement. Is this southbridge error a possibility or was he talking bs to get me out of the store. And in either case does anyone have a fix for a broken nub and mouse buttons?