Can working on the computer before bed effect my sleep?

Yes, overstimulation. The sleep-wake cycle is linked, in part, to external light cues; staring into a bright monitor screen at 3am is one way to throw off your biological clock with great ease. This, coupled with the increased stimulation involved with watching movies, listening to music, reading news, etc. Is simply not conducive towards initiating the sleep process.
yes. In a really destructive way. Give yourself 45 min off computer before bed time.