Recommendation from the B4D Forum:

While most people go to the computer supply stores at Rua da Informática in CLN 207/208, there is a much better shop in CLN 406, Bloco E, called InfoStar.

InfoStar is a wholesale IT supply store that also sells to the public. They stock everything from computer parts like hard drives, memory cards, motherboards, power supplies, sound cards, CPUs/Processors to hard core gaming equipment and cables. And if they do not have it in stock, they will get it for you in a very quick time.

Another positive aspect of the store is that their commercial director, Alexander Ferreira, speaks perfect English and he will be more than happy to help you find the right parts, equipment and give you advice on how or where to fix problems on your computer.

I personally shop there for all of my IT needs and so far they always delivered excellent service and all their parts come with guarantee.