Doing a clean install of Mountain Lion.
Basically all you need to know is contained in this
I decided to make a bootable usb thumb drive, following the instruction
However, when I used the Disk UTILity to prepare the usb thumb drive, an error message ‘Could not Restore. Invalid Argument’ came up.
Turns out the thumb drive works despite the error message.
Now I am restoring my files from the time machine copy.