Snap. Pretty much to backup any files you want, you can either put them on a second hard drive in your computer (If you have one), or put them on an external hard drive (If you have one). Don't back up any of your local settings and such, just your documents, pictures, and music/movies. If you don't have another hdd or an external, then you have to backup your files onto a DVD (THrough will probabbly have to use a few).
Once you have backed up your files (If you can, or if you are happy with loosing everything, then continue), you need to reinstall your OS... Make sure you have the windows instalation disk, and any driver disks that came with the computer.
Inseart the windows disk! Restart your computer. Depending on the computer, it might have a "Boot Options" when the computer first turns on. You will have to press either f10 or f12 to access that. if it has, then select "Boot from CD/DVD drive". If not, then you need to enter the Bios (Press f1, or f2, or del, or all three at the same time if you are unsure which one it is), and go into advanced Settings and change the First boot device to CD/DVD, and the second to Hard Drive.
Once the above is done, it will come up "Press any key to boot from CD" when you try to start your computer with the Windows Install Disk. PRESS ANY KEY!
Then format your hard drive, and install windows. Its not rocket science... Just follow the promts.
Once windows is installed. Inseart your driver disks, and install all the drivers... Done... + you can download stuff for it like Adobe, flash, java, MSN, anything else you need.
If you are uncomfortable with doing that, take it to a Pro.!
