My mc75a will not accept my credentials - Motorola MC75

Neither me nor anyone on fixya has anything to do with your "twic card", whatever that might be, or any US GOV agency and the procedure to get you accepted for it..
Contact the proper website
http://www.tsa.gov/stakeholders/transportation-worker-identification-credential-twicR

Contact Motorola Solutions. Http://www.Motorolasolutions.com/support or http://www.zebra.com/support. Mark Motorola Support

Can You use the buttons? Press the right button with a white bar, just below the screen. This should open the Tools menu. If it does, use Exit and leave AppCenter. If this works, You can test if the touch screen is defect or if AppCenter installation is corrupted. If the screen is ok, reinstall AppCenter.

Press the #1 and #9 while turning on the device.

Firmware update

How do I log in?
Initial access to TWC WiFi requires the user provide log in credentials that identify the user as a current, qualified TWC Residential or Business Class customer. Credentials can either be a TWC ID and Password or Time Warner Cable email and password.

1. First, make sure you are within range of a TWC WiFi Hotspot and that the WiFi feature on your mobile device is turned on.
2. Select TWCWiFi from available wireless networks.
3. Open your browser. The TWC WiFi Connection page will appear.
4. If you're a Standard Internet customer or above, enter your credentials. You can either use your TWC ID or your Time Warner Cable email and password.
5. If you're not a Standard Internet customer or above, request a 30-minute free trial or purchase a TWC Access Pass for as little as $2.95/hour.
6. Accept the Terms of Use, click Submit and connect.

press power on and keys 1 and 9..

Download here at motorola:

http://www.motorola.com/Business/US-EN/Business+Product+and+Services/Mobile+Computers/Handheld+Computers/MC75A_US-EN#support_tab

You need adobe reader to read the content.

Good luck

http://www.motorola.com/web/Business/Products/Mobile%20Computers/Handheld%20Computers/MC75A/MC75A_Spec_Sheet_0310.pdf
Enjoy!