How to Factory Restore Inspiron 530 Desktop without Windows Vista Installation Disk

Hello, Everyone!

I have been trying to factory reset my desktop Dell Inspiron 530 with Windows Vista Home Premium for so long. I have tried the "Repair Your Computer" option in the F8 Advanced Boot Options when I restart it, but it just resumes normal start up. I have also tried to restore to an earlier time but it doesn't have any saved! I would really like to restart fresh without having to buy the Installation CD or anything else. Help?