OK, If you have actually formatted the drive and tried installing system 3 times my guess is your BIOS chip is probably infected.
This is assuming you have not tried to save and reinstall any files of yours from the previous installation.
That means if any CD or memory stick that you have taken some of your old files to save (photo's, files, or what ever) are not being put back in. They are reintroducing the infection if you are doing this.
If you are doing this clean and properly then you have a very nasty bug, probably it is above your pay grade for removal :)
There are some tricks to try and get it though, so try the following.
You should unplug the tower and remove the CMOS battery then CLEAR the CMOS by shorting the pins on the motherboard, leave the pins long enough for any residual energy to dissipate from the board, we are hoping this may cause the infection to lose its hold but doubtful.
Then try format and reinstall the 4th time. If this fails you will have to check out the Motherboards Model#/Serial# and download a newer BIOS file if they have one up for an offering, or just get the same one that is presently being used.
What may work is to Flash the BIOS chips code file.(reinstall BIOS)
Your Motherboard manufacturer should have the BIOS file and instruction on using the installer.
(Bios Flash Utility or BIOS Flash boot CD) Do Not try Windows Flash Utility.
Be warned if you try this with an infected Windows chances are it may fail and your chip could end up making your Motherboard into a paper weight.
Obviously it has windows number.
You could also try installing a Linux Distro to check out further.