Good advice from GreyCatz but it might be a bit brutal on your personal files. Try mashing the power button every time it starts up and sooner or later it will offer you StartUp repair options.
One of those will be Command Prompt and since the loop is sometimes an indication of hard disk problems, use that command form to run Checkdisk.
At the prompt, type chkdsk c: /r
and hit the Enter key. It will take quite a while but let it go to the finish then restart and if there's no difference, go through the same process to get to Reset or Refresh. Refresh swears it won't interfere but has been know to do just that. Reset will definitely delete them all.