virtualbox.org

I been using a install of Windows XP service pack 2 for a while, and then all of a sudden the windows will no longer boot. It will resize the window, and then crash and start to boot up again. It will keep doing this over and over and over again. The windows machine will bootup in safe mode.

Does anyone have any idea what is going wrong, like where to look?

This can happen if the VM virtual hardware changes, e.g. you change disk controller type. It can also be caused by changing hosts (which may change CPU type). Have you made any changes along these lines?