Why could Nebuchadnezzar's magicians not help him with his dream?
They could not help because Nebuchadnezzar had dreamed a dream and then lost it. When he tried to get his magicians to bring the dream back, they could not do so at all. No further explanation for their inability is supplied.
Les explains that Daniel is writing shortly after Nebuchadnezzar besieged and took the Jews captive out of Jerusalem and Judea back to Babylon. Daniel, a young Jew trained by the Babylonians for service in the king's kingdom, was brought to preeminence by interpreting the dream Nebuchadnezzar had dreamed and lost. The king tried to get his magicians to bring the dream back, which they couldn't. Les notes that scoffers ridicule Daniel, claiming it was written by an imposter long after the events, rather than by this young Jew writing before they happened; he recalls a class question about proof and turns to Matthew 24. In the immediate account, the magicians could not recover the lost dream, but Daniel later interprets it.