Aren't there two latches (or whatever) on the hood? I closed it once and only one side latched, the other I had to press down on to get it to latch.
After getting my oil changed I saw them do the same thing, but other side.
Now I just make sure that I close it with a bit of force (as others have said a lot already).
Now if something's stopping/hitting it, then that's a different story. Get out the dremel or sawzall...