Dear maisie46,
Glad to hear that you did not call them. But I had to make you and other users aware, just in case.
If article about sign in option did not help, then it would be better to try fill out the recovery form:
1. Go to account.live.com/acsr.
2. Under Email, phone or Skype name, enter the info for the account you need to recover.
3. Enter an email address that we can use to contact you about your account recovery.
4. Enter the characters you see on the screen to prove you're not a robot, then select Next.
5. A screen will pop up asking you to verify that email address. We'll send you a security code in an email. Enter that code, and select Verify.
6. Now you'll be asked to answer several questions about yourself and your account. Fill in as much info as you can, even if you're not sure. See Tips for filling out the recovery form below.
7. Select Submit when you're finished.
More about validation procedure you can find here
https://support.microsoft.com/en-us/help/10494/...
If he still will not be able to recover account, try to contact Microsoft Account support directly.
I hope he will be able to retrieve his account.