There are several computer labs and terminals around campus, many of which are 24 hours. However, these labs can often get packed around midterm/finals season, so it's good to know about some of the less-popular locations in order to ensure you can snag a seat if need be. That being said, most students have their own computers so you're never battling the entire Columbia population for a computer.
Printers at Columbia are notoriously faulty, with some locations being broken down about 50 percent of the time. Therefore, a good tactic is to "print" to several locations to make sure that you will be able to actually print your assignments. Printing stations also fill up right before classes, so waiting to print your essay right before class may not be the best idea.