@Syaoran No, that's almost impossible. If there's a way that you can earn some money with your spare computer, everyone would be able to earn the same money in the exact same way. Then it becomes meaningless.
@Syaoran Any devices that consume much electricity would be expensive by themselves. An i7 with a decent graphic card, maxing out 24*7, will only use 15-20 kwh, = $2 per day. You'll have very little profit if not less.