The easiest way to do this is to download the Wan/LAN drivers off of the manufacturer/suppliers website and place them on a USB drive. I also recommend placing spyware and AV programs onto it as well. Place the USB drive into your reformatted pc and install the driver and AV programs. Once this is completed you can download and install everything else as needed. I wish I could have gotten to this post sooner, I may have been able to assist you in discovering what the problem was. More often than not malicious programs will first write a start once registry entry into the local registry that will attach an executable to a legitimate Microsoft service such as svchost.exe (your machine will be running many instances of this program). The next time your pc is restarted the run once entry is ran during the STARTUP phase this is when the actual piggy backing occurs. Once it has reached this point it can bypass windows security and start doing what it wants (this is how many back-door attacks and Trojans work). It is at this time that a permanent registry entry is added that will run the malicious program on each and every start up. Now is when you should be able to see the program in question running as a service. More often than not it is possible to trace the malicious service to its host file location. From here we can isolate the files and learn a bit more. It is even possible to view the .exe (along with the other files) to see what registry and service it is altering/hijacking. From here we can boot the system in safe mode, remove the offending registry entries (to prevent the program from making copies of itself), then the file themselves could be removed. It can be along process if you are unfamiliar with registries and how the windows security platform is ran. I will highly suggest checking out some other forums that may offer more assistance. For example one of my frequent hang-outs are the Hak5 forums (I'm not sure if I can link to other forums so I'll leave it out for now) where you can find several A+ and Microsoft certified individuals who will be more than happy to help. Not saying that there aren't intelligent and capable people here, there are plenty as you have seen! But occasionally other forums are more suited to this type of problem.