Best way to reformat PC?

Hi, I'm a computer newbie. For the past month, my PC has been infected with a virus, cleaned with anti-malware programs, and re-infected again repeatedly. After browsing around for solutions, it seems like I have some "backdoor trojan". So, I've decided I want to reformat and wipe everything clean, making my PC 100% virus free. However, I have a lot of concerns about it. I'm worried that the virus will survive any reformatting as I've heard there are some boot sector viruses. I also don't know the "correct" method of thorough reformatting. I've heard about using disk cleaning utilities, zero filling, boot and nuking, low-level formatting, and manufacturer formatting and I'm not sure the way to go. Also, I lost my OS disk. Can anyone please help me? Thanks so much.

My computer specs are:
Microsoft Windows XP Professional Version 2002 Service Pack 2

 

Probably one of the reasons you got reinfected is you are still using SP2 which no longer is supported by Microsoft and does not receive security updates. You should have updated to SP3 long ago. You can post in the Malware Removal Forum and attach your logs according to the stick post. They should be able to clean your computer and then you can install SP3 along with some additional security software.

One option you may have is to recover the OS to a factory state if you have an OEM computer like HP or Acer using the Recovery Partition if it is available.

Low-Level formatting today basically means to zero out the hard drive. Because you do not have a Install CD, you will not be able to install XP after you zero the drive.The only option available would be a linux distro like Ubuntu. Or purchase an OEM XP disk on ebay.

You can zero out the hard drive a number of ways. Seagate has Sea-Tools for DOS. You can create a bootable disk to zero out your hard drive. You can also use the bootable version Partition Wizard to wipe the disk. Both are iso files that need to be burned to a CD with Imgburn (freeware) or Nero. If you zero out the hard drive, you no longer have to worry about a virus of the MBR. The MBR will no longer exist.