I need help. Please read!!!!

yesterday I downloaded a rar. file I went to open it and I started to get pop ups for a program called pcdefender. right after the pop ups started I noticed my Mcafee was disabled and then my internet connection was lost on that computer but my other computer running off the same router is working fine. I ran a virus scan and quarantined or removed all the viruses but my internet still wasn't connecting. I went to nero to make back ups of some important programs I have on this computer but it will not let me burn anything to disc. I stuck my windows xp operating system disc in to try to run the repair program and now that it completed my computer just keeps restarting before windows can even launch. can anybody please help me. thx in advance