Question: how much electricity does a computer screen use?
Answer: Given that the average North American household uses about 1000 kWh/month, if your monitor were in actual use all month (720 hours) at 40 watts it would use 28800 watt hours or 28 kWh. About $3 to $5 depending on your power rates. Most monitors are set to go to sleep after a few minutes of inattention.