Let's share all methods available for accessing your account, @RUSHHHHHHHH!

As stated by @formerlyknownas, you could have put the SIM card in another phone to temporarily get service while your phone is repaired.

As long as you're the account owner or an authorized user on the account and know the passcode, you can visit your nearest AT&T Store or contact our customer service to retrieve or update your account information. The store locator can help you find a location if you're unsure where one is located. Our contact information can be found under the Contact Us tab on the wireless support webpage.

We hope this information is helpful.

Ashley, AT&T Community Specialist

I made a mistake in typing my question.  It should read : 

How do I access my att user account, if my cell phone is not functional, etc.

You can use your computer or laptop, go to att.com. Goto my At&t and then sign in, you will need to enter your username and password

JayNice, 

Thanks for your response, but I don’t think you correctly understood my question.  I have already used my iPad to try to sign into my ATT account at ATT.com.  After entering my username & password, Then tapping “sign in”, I am taken to a screen that says “Lets make sure it’s really you.  We need to send a code to your ATT cell phone.  Then you can enter that code to confirm your identity, and we will sign you into your account.”  But since my cell phone will not even boot up, I cannot receive this code, and therefore, cannot log in to my ATT online account.  There is no option given to allow the code to be sent to my email address that is registered with ATT.  So, I am wondering how I can successfully log in to my ATT account.

You didn't by any chance remove your SIM card from the phone that's being repaired did you? Service and your two-factor authentication text is sent to the SIM card not the phone. The phone is just the means for the SIM card to function.

Usually we suggest people take the SIM card out and put it in another AT&T compatible phone to receive the two-factor authentication text. But if you do not have the SIM card, that's a problem.

You could have put the SIM card in another phone to temporarily get service while your phone is repaired.  (If there is an insurance claim involved, you had to make an insurance claim prior to switching your SIM card)

You will not be able to log in online without to factor authentication. You would have to contact AT&T directly and provide your security PIN code in order to access your account over the phone or in person