before you start formatting or doing things that erase your data, take it to a computer shop. If you live in Melbourne, I can refer you to a good shop.
If you have never seen inside a computer, then this might be too daunting. Anyway, unplug the cord from the back of the computer.
Take off the cover. its the panel on YOUR left side. There is a bolt like screw half way down. Unscrew it. It is removeable. Don't lose it.
Locate the CD/DVD drive. Take note how the ide cable and power cable are plugged in. Write it down. Uplug the cable and cord.
Put the cover back on, no need for the screw, its in case you accidently put your foot inside.
Put the power cable back into the back of the Power supply
Remove any extra devices from usb ports like a camera orphone or flash drive.
Turn on the computer. if it works and you got something happening then the power supply is inadequate.
This is where the other guyas take over
You need to update the ram to at least 512 mb. The video has to be the same brand otherwise it bugs everything else and at least 128mb.video ram.