When powering up the tower, all I hear is the fans running full speed and I never hear the ''beep''. The system never comes on. Nothing on the monitor, etc.

Is this a brand new system? If so, maybe components not correctly seated inside, ie CPU or memory not seated correctly.
If this isn't a new system then in my experience it is most likely a power supply or motherboard issue. Hopefully power supply as this is normally the cheaper component of the two!
Hope this helps.

I agree with the previous post. First open the case with the unit plugged in to the wall. Before you put your hands inside, unplug the power plug. This will ground you to prevent electromagnetic shock to the components. Next with two thumbs remove and re-seat the system RAM. One or both chips can creep out of the socket. Experiment and start the pc with one chip and then the other in case one is bad. If the RAM does not fix it, any short will prvent the pc from booting. While you have the case open, Remove all add in cards. This includes, modem, sound, network, video, etc whether it is a PCI, PCI-express, or AGP socket, When powering on you should then get a beep for video missing. Replace the cards one at a time until it quits working. AS the last resort I would replace the power supply. To replace it you need to tell us what name brand, model, or open the case and copy down the name model and power in Watts it uses. You may find this video helpful http://www.youtube.com/watch?v=DLxNPBQBfT8