The signs don't bode well for your computer. It's quite likely that the power supply unit, motherboard, or both are damaged at the very least. It may well be that your hard drive is also damaged but you can rather easily find out by doing the following:
* Remove the hard drive from the system
* Change the drive jumper from 'Master' to 'Slave'
pop the drive into another computer as a secondary drive, copy your data across if possible and burn it to CD.
Of course, you may not have another PC there to use but adding it to a friend or work colleague's PC as a secondary drive is a handy and cheap way to do things. You can remove it once you've lifted your data files off it and backed them up to CD or DVD.
Your computer itself sounds very much like it needs to be inspected for damage by a technician, I'm afraid. I would certainly advise backing your data up off the hard drive before that happens. Technicians often have a horrible habit of formatting your hard drive and reloading Windows cleanly, and you'll lose all your data for sure if that happens ;)