"A computer"
"Una computadora" is one of the regional expressions for "computer". Others can be "un computador", or "un ordenador".
Is there a computer in your class?
As a statement it means "you have a computer" As a question it means "Do you have a computer?"
¿Tiene usted un ordenador/una computadora? -formal ¿Tienes un ordenador/una computadora? -informal
"Is there a computer in your class?"
Es sólo una computadora.
To say 'I want a computer' in Spanish, you would say 'Yo quiero una computadora.'
the student (female) wants a new computer.
You say, "Trabaja por una empresa computadora."
Well, darling, "una computadora" is the singular form of "unas computadoras." So, if you're looking to talk about just one computer in Spanish, you'd say "una computadora." Easy peasy lemon squeezy!
La disquetera es el dispositivo o unidad lectora/grabadora de disquetes.
The statement is "Fernando has a computer". If he has one, you would say "sí". If not, you would say "no".