winlogin.exe error????

hi, i just got windows 7 ultimate and i keep getting two errors that pop up around 4 times, winlogin.exe in which the file area in which it says its in does not exist and it keeps saying that windowsexplorer.exe has stopped working. help! also my anti-virus(mcafee) keeps picking up different trojans so do i have a trojan downloader? help plz!!

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