Windows 7: startup problem

aoa
guys my dads freind just inserted his usb ito my dads pc nad guess hwat it restarts on every startup
the only mode i can run it in is the debugging no other method works
i have already tried startup recovery and system restore but no luck
i did clean install of windows twice but after 2 normal boots the windows restarts at the orbs in the startup plz help
what should i do
i checked a diagnostic report
and it said error 1 oly in system 32/kytsag ...... file
if anyone of u can help
there is no minidump file either in the swindows folder what the hell has happened
i formatted the c drive and completely reinstalled the win 7 ultimate but of no luck
can anyone help me witht his virus or whatever this
p.s i tried to to do bootloggina nd at one specified log file it restarts what is this?
plz help

sny suggestion is welcomed