excel should have no problem with this kind of nonlinear optimization, check the formulae you put into the cells, make sure you are using "minimizing the portfolio variance by changing weights subjecting to constraints of (summation of weights)=1 and every weights>=0". (second constraints = no short sell) 

yup, I have done all the requirements you said, but I found it is not really reliable. you could copy the excel form, then use other computers to open it, the result of the weights for the minimisation of variance showss different. yeah it might be many solutions.

I wanna know, does anybody learn Matlab by themselves? at least from the basics?

or you guys have got some lectures for that.