Computer repaired and returned with different fault

I recently purchased a new E5-411, installed win 8.1 and everything worked fine until after a few months the computer wouldn't turn on. I made a five hour journey to the Acer repair centre in Phuket (Thailand). They replaced the mainboard but when the computer was returnd to me the touchpad wasn't working, the engineer said I would need to reinstall Windows. I travelled back to where I live a spent many hours reinstalling the o/s by various methods eventually doing a clean install on formatted and newly partioned hardisk....still the touchpad didn't work. I phoned the engineer at the repair centre and he said that because the mainboard had been changed my original Windows would no longer work and I would have to get them to do reinstall at any local computer shop. This doesn't make an sense to me perhaps someone can enlighten me.

There was an update to the bios for this model on the Acer support site, a fix for problems with the touchpad and win 8.1, I flashed this but TP still doesn't work.

Another thing I discoverd is that my original s/n was NX.MLQST.002 now it has changed to NB.MLQ11.00A, although the MB model and version are the same (EA41_BM type 2-A01). Could this be the source of the problem? The NB.MLQ11.00A replacement seems to have been produced earlier than my original MB. As my machine is under warranty why didn't he replace it with another NX.MLQST.002. When I enter my old full s/n in the Acer support site search my model Aspire E5-411 comes up in the results, when I put the changed s/n in it comes up with no results. Can anyone explain what's going on? 

Thanx in advance

brogreg

As you suggested I emailed head office and they contacted me and they will take it in again for repair but at a different service centre. Head office contacted the service centre and I will arange to have the computer dropped off. They agreed to change the replacement board to the MB with the same s/n as the new machine and hopefully get the TP working. Thanks for your reply.

Greg