你有一段时间没上网了用英语怎么说？

You haven't been online for a quite while

you have not accessed the internet for a period of time

It's been a while that you haven't been on line.

It has been a long time since you used the Internet.上面的都不对

You haven't appeared online for a long time.

You haven't been online for quite a while.
比较赞同LGCorvallis的答案，是最常用的说法。只是“a quite while”改成“quite a while”更准确，呵呵。