HELP-Can't remove old security syst fragments

Hello,
I just installed a Kaspsersky Internet Security System and when it "uninstalled" the very bare bones McAfee system I had, it did NOT get all the fragments. My computer became crippled, the Kaspersky "protection" is not working. Until the fragments are gone, it will stay like this. Two days of hell dealing with Kaspersky Techs - eveything they suggest is not possible or doesn't work. My computer is now open to viruses, etc. -- the Kaspersky system doesn't work until the fragments are gone. WHAT DO I DO -- ERASE MY WHOLE SYSTEM & REINSTALL. I'm scared to try that as I'm no computer whiz.