"una computadora" is correct above for Latin America. In Spain "un ordenador" is used and this has probably caused the confusion, so that "un computador" is now also correct in some places in Latin America. I am willing to bet that it may be different from country to country. https://dictionary.reverso.net/english-spanish/computer http://www.wordreference.com/es/translation.asp?tranword=computer
Yes, there are three different words in Spanish for computer.
“Yo” is not required and subjects are often omitted in Spanish. “Necesito” is probably available. There will always be one possible answer that you can make. The answer above is not the only answer, and it is not even the preferred answer. It is just one possible answer.
Is the problem pronunciation or microphone?
Try listening to native speakers and practice repeating at Forvo.com
For microphone problems: https://support.duolingo.com/hc/en-us/search?utf8=%E2%9C%93&query=microphone&commit=Search