Just installed Win 8 64 bit version, and soon afterwards added latest version of FBackup - 126.96.36.1996. Have used earlier versions on my just replaced pc and never had problems like this one.
Now each time I run, either on scheduled or on manual backup, I get the warning screen "do you want to allow the following program.... etc" and If I say Yes, the hard drive light immediately goes on for the next 15 minutes, and I can do next to nothing. No response to keyboard or mouse. If I start with Task Manager active, I can see nothing consuming all, or even most of, the resources. After the 15 minutes of constant hard disk light, it finally starts to flicker occasionally ,then the familiar FBackup screen pops up and the backup begins. Backup then proceeds normally and finishes without problems.
I often run FBackup while Firefox is active, and sometimes that gets tagged with (Not Responding) during the dead 15 minutes, but running FBackup without starting Firefox still causes the 15 minute hang.