I think it's suppose to be 学校に行って、パソコンを使った。In this case, you use the -te form to 'link' things together such that the second part follows the first part. For this, meaning: I went to school and used the computer. It's the same as 学校に行って、パソコンを使いました。, which is more formal.
If you write 学校に行って、パソコンを使います。, it'll mean: I will go to school and use the computer (there).
pasokon -> personal computer
konpyuuta -> computer
both means the same thing, generally.