That suggests that the problem is local to your user account rather than is system wide.
First thing to do is start up in Safe Mode, then go to
> System Preferences... Users & Groups | Login items
Remove everything in that list, then restart the mac normally and see if it boots.
If not, post back and will look at a few other places that might be
Have you tried setting up another user account and seeing if it still acts the same? A follow up to softwater's thought.
Here is another thread with some other suggestions:
If you monitor the "More Like This" box, perhaps you'll find a thread that will help.
I did something better; I erased the disk and did a clean install of Mountain Lion. (I had previously bought a new disk becuase I though that it might be a disk failure). But I still get the same problem. In fact I got the problem during the install. But I could finish the install doing safe boot. Again, I can do a safe boot, but not a standard one. And this occurs before the login.
The hardware check from the original disk says that there are no problems with the hardware.
I will now try a clean install of Snow Leopard and see whether that works.
I'm guessing that it is a hardware problem, because Mountain Lion has worked fine for a few months. But I've no hints as to what it may be.