Recently my computer has been sporadically freezing on startup. It freezes at the login screen. Sometimes it freezes immediately and I get no mouse movement, sometimes I manage to get mouse movement, and sometimes it freezes completely when I press enter (to login). The thing is that this problem is quite infrequent. I happens maybe around one in ten boot ups. It also leaves no trace in the Windows Event Viewer. Because it freezes here it makes it very hard (in my opinion) to troubleshoot. Any general advice about how to solve or investigate further a problem like this?