If you spend a lot of time with computers during the day, a dream that you are using a computer may simply mean that you are carrying over stress from school or from work into your dreams. If this is the case, try to spend more time relaxing when you have the opportunity. Try to engage in more physical activity and spend more time outside.
A computer in a dream can represent your own mind. It can be a representation of your memories or of your thought processes. You may dream about using a computer when you are trying to sort something out in your mind or when something in your life has occurred which is causing you to bring up repressed memories.
If you dream about a computer it can be a message that you should approach a problem more logically.
A dream that you are using a computer but it is not working properly can mean that you are not thinking clearly.