Touch pad mouse

I had problems with letters T and G,on off,for quite a while. I bought a new keyboard and went to a professional IT man who fixes laptops for a living. He opened the laptop and there was lots of dust inside. He cleaned it with a small brush,changed the keyboard but it wouldn't work. The mouse was working as normal. Then I left for an hour and he changed the keyboard successfully,but when I went back the touch-pad laptop mouse was now not working. He told me dust may have got inside (my fault,though it did work after he dusted it off!) or the circuit (inside) got broken and he could do nothing.It is impossible to fix it,according to him.
He charged me for changing the keyboard and gave me an external mouse as if it was all right. I feel terrible that I went to him with a working touch-pad mouse and got out with a broken one. I find it tricky to work with the external mouse and am feeling very down about the whole thing. What may have happened,how and why? I so desperately want my old mouse to work and not to carry the new one around with me.I feel like crying.Last night I woke up several times and wanted to cry.