Help me to get rid of that

[auroraalpha]

I am a beginner. One of my computers ( AMD athelon processor, RAM 1.2 GHz ,XP OS) had no antivirus and now it had been severely infected. A black command prompt window appears at starting with warning of one dll file. Attempt to install norton and Panda software are terminated with drop down of current window. Attempt to view hidden files and folders and open scheduled tasks are terminated with drop down of window. ( I had installed Norton 2005 previously and then remove with Uninstaller software). I copied some suspected files and scanned at another computer having Norton antivirus with update. 140 files was infected and most are with W32.Rontokbro@mm, and others with W32.elkern. I downloaded removal tool for Elkern and Ran it in infected PC in safe mode( as directed). Removal tool was extracted with difficulty and finally it scanned the PC. Report after scan as 24 files had been repaired with no effect on registry and others. But after it, no apparent good change to PC. Norton and Panda tried to install but installation window dropped down. Then attempt to restart in safe mode is inhibited(window quickly drop down before making complete changes in utility)
Please help to know whether there are other unidentified thread or Elkern not removed properly or Rontokbro making these problems. Please advise to solve these and advise way to install antivirus in such circumstance( please remember I am still beginner).