ADP has some help for getting your W-2 Online.
Click this link to see the help page.
If your employer has intentionally locked your account, that may not help.
The IRS can also provide some help. Go through the steps provided. The first step is to contact your employer. It may help to let them know that you are going to call the IRS next, if they won't help you get your W-2 form.
Click here to see the IRS advice and contacts.