someone mentioned that there should be a recovery partition on your hard drive.
basically with company built computers (including laptops/netbooks) you will have a section of the hard drive the is inaccessible whilst in windows. its designed so that you can restore the computer back to the original form when you got it. usually its available as a shortcut within windows... if ur not as fortunate then you'll have to hop into it whilst ur system is booting up.
common names include: recovery mode, restore factory settings, format back to original options. or any combination of these.
the more advanced and not recommended method is to copy a windows CD onto a USB drive and plug it into ur laptop. this will install a generic version of windows onto your computer but not necessarily all the drivers required for your computer. (drivers are software required for individual parts of the computer to interact with itself)
when your computer boots up it'll automatically select something to startup, this includes ur cd drive, hard drive, floppy etc. if you have a USB plugged in, you can tell your computer to boot up using ur USB drive. this must be done usually within the first 10 seconds of powering up.
ok i dont think this makes sense so holla if needs clarification/explaining. prob do it for you if ur in melb and havent sold it already lol