It is really tough to say. Most computers use around 300 watts of power running full tilt. Meaning the monitor is on and the hard drives are spinning. With the advancement of power saving hardware, firmware, and software that number is probably high. I have seen computers in "sleep mode" that use only about 25 watts and I have seen others that use 400 watts. It all depends on the size and configuration of your computer. Anyway you look at it, you are only paying ConEd pennies a day to let your computer on. For example, a 300 watt usage running for 24 hours at $.07 per kilowatt hour will cost you about $.51 per day or about $15.00 per month. However, I will say that leaving a computer on continuously can be very hard on the harddrives and other components. Kinda of like letting your car run continuously. Hope this helps.
Hi, Virgil: I agree with what you said about keeping the computer on 24/7. I asked the people in IT (the Information Technology department at the Junior College where I work...we have a lot of fun with the name of their department around here... ) and they told me that leaving a computer on continuously is good for it; less "surges" during startups, keeping the equipment warmed up helps drive moisture out of it (down here on the Gulf Coast where I am), as long as it's powered through a good surge suppressor. They did some unofficial research and found that computers in student labs (which are left on 24/7) held up better than those in faculty offices (which are typically shut off at the end of each workday)...sounds kinda like the thread that appeared here some time ago about the virtue of leaving fluoresent lights burning continuously. Apparently the money saved on maintenance is more than the money spent keeping them powered up full-time.
I ran a bbs from 1986-1997, the computer ran 24/7. I had to replace the power supply fan a number of times and I had a hard drive that would not spin up on its own if I did turn it off but aside from that, the mother board, memory and all the rest of the parts lasted. I had a hard drive fail with bad sectors after 5 years of use, but that is typical for the drives made in the mid 80's. It cost me an extra $20 or so a month to run it. Once the internet came along and local boards were no longer needed, I took it down but I still run 2 computers 24/7 now and have been since I took the bbs down. No problems at all, I do have everything running on a big APC. I have had modems die over the years from spikes, but never the computer. I work in the IT field for an insurance company,(500 users) we use mostly compaq deskpros and have video cards die all the time on the users machines, never have any problems with the servers. I would leave them on if it were up to me and just turn off the monitors. But then, we turn off the computer and leave all the lights on...go figure.