Can the work on or light from a computer mess up your circadian rhythm?

Yes. The bluish color emited by computer monitors, tvs and other screens supresses melatonin production. Melatonin is your body's natural sleep hormone; it helps set your internal clock. When it is supressed you don't feel sleepy or sleep poorly. If you are bothered by computer work or tv watching simply turn off the devices 4 or more hours before bedtime to allow your body to release melatonin.
Yes. Light in the blue wavelength spectrum can definitely affect the circadian rhythm and working on a computer late in the evening can make it difficult to fall asleep.