my destop was working fine and i shut it down every night like I always do by clicking turn off. The next day we tried turning the pc back on and the monitor came on but the brainbox will not power on at all. what do you think is wrong with it?

Any Beeps.
Any Hard Drive /Cd Drive activity.
Any info displayed on the monitor.
What is The OS ?

any fans working? If so, are they all working?
any lights, monitor, hard drive, CD/DVD, power switch?

No fans are working on it. I dont see any lights comming on at all, no power to the box at all, the monitor powers on though.

I do not hear any beeps, the box wont power on at all but the monitor will power on is the only thing that I know.

Do you get a message on the monitor?
Is the power for the monitor direct or through the power supply of your PC?
From what I understand of your problem you should get a message on your monitor like "No signal"
The most likely cause of your problem is a faulty power supply. (assuming that you have everything plugged in properly). It is one of the cheapest parts to replace. If you want to you can follow the directions in this video and see if it is the cause.
http://www.metacafe.com/watch/729606/how_to_test_your_computers_power_supply_psu/