Just check these things first:
Any lights on the front of the tower?
Any fans going round?
There should be 2 lights on the front - one for power the other for the hard drive. The power light should be permenantly on and there's another one for the hard drive. The hard drive light is usually red or orange and flashes when something's loading, so I'm wondering if this is the red light you meant in your first post. The power light is usually green but depending on your tower it may be a different colour. If it's a black tower the light may be blue.
If you can hear the fans and there is one beep and the hard drive light starts to flash, it means it's loading up Windows as normal and the monitor has either come unplugged or there is a problem with the graphics. If there are no fans going round it could be the power supply (the bit with the fan and where the power cable plugs in) and these are quite cheap to replace. If the fans go round and there are no beeps then nothing is loading and it could be the motherboard and it might need replacing. Either way you can change these bits yourself or if you don't feel confident in doing it, you can take it into a shop and they'll do it. Remember a computer never dies, you can always change the parts that are inside it ;-)