There are some sleep settings in most BIOSs. However I don't think that's your problem.
Did you try unplugging the mouse? Try a different mouse also. That may tell you.
It could also be a network sending packets preventing the monitor from turning off. If your monitor NEVER turns off there is something resetting the timer. You have to find out what it is. This is a frustrating problem.
If your monitor shuts off then turns back on seemingly randomly, it's probably your mouse or network. (or other input device)