Try retrieving your IP Pin late at night or very early in the morning when the IRS Website has less traffic. Unfortunately, the IRS Website usually has a lot of issues at the beginning of the filing season. You can also contact them via phone for the IP Pin, but it can take up to 21 days for you to receive it in the mail.
Check out more details about getting your IP Pin in the Turbotax FAQ below:
https://ttlc.intuit.com/replies/3388576