My question is my Dell Optiplex 620 is not working properly !! when i turn it on it goes automaticaly to bios and says click on safe mode or safe network or best last start up or normal mode ?? but when i click on normal it comes back to that window then i click on safe mode and it works for about 5 min then it reboots its self every time what can i do ? i checked if there was a virus and its clean !! please help