It has been more than a month and my son has not received his tax refund. He direct deposited it in to his checking account. How long should it take to receive his refund. Could there be a problem?

If he filed by electronic means he should have had his refund within two weeks. He must have filed by mail.

If you e-filed and opted for direct deposit, you should get refund within 2 weeks. To check status of your refund, read:

Your U.S. Tax Return: When will I get my tax refund?