Tommyek, I was working in the office all weekend. In the example above there is no interruption of the action as there would be in a sentence like: I was working in the office when the phone rang. We can use the Past Continuous simply to talk about actions or situations that went on for some time in the past. I was working in the office all weekend. In this case when the action started or ended or exactly how long the action lasted during the weekend is not important to the meaning of the sentence. The cats were fighting last night in the court below my apartment. Yesterday I was watching the televised match between Zenit and Spartak.

'I was working...' is past continuous. You use it when you were doing something at a particular time. "I was working on my homework when the doorbell rang." "We were driving to Pittsburgh when the storm came." "She was riding when her horse fell." In the case you give, it should be "I worked in the office all weekend.", because the action was completed in the past and is not compared with some other event or time.