How do I insert SIM card to Toshiba tablet model no AT7-B

this tablet don't use a micro sim card just a micro SD card (memory card)

Some tablets do not incorporate mobile phones - check your apps for the manual or look here with your pc

Toshiba AT7 B8 Android 4 2 Jellybean User Guide for Excite AT7 Series

Notification option may over ride in some tablets.
Do cold restart of the device to hear startup sound.
I would also consider verifying the latest firmware.
http://support.toshiba.com/support/viewContentDetail?contentId=4006098

It wants a passcode to be entered! Can't you remember the passcode?

If you have no wireless service available or hotspot to use. you can by a device such as Truconnect. It is about the size of a credit card and gives you private service to connect to your device. It is a use as you go deal. You load it up 20 bucks at a time and when your usage is about up it will automatically reload from your credit card . It connects to any wireless device just like you would connect to a router.

1, Make sure that the device is turned off. Pull the card tray from the left edge of the device.
2, Take the tray out and insert the SIM card into the slot. Check if the card is inserted properly.
3, Press the tray until it snaps into place.

To insert Sim Card in a Panasonic CF-H2, you need to open battery compartment 1 and remove battery, you will see where the Sim Card inserts, place the sim card gold side up in the depression. Slide sim card down the depression toward the sim slot, slide down till it clicks in place. Re-insert battery 1. Sim card inserted.

This model tablet supports MicroSDHC memory card.

Hello friend

(("You must remove the battery, then insert a SIM card into the 3G SIM slot toward the right of the battery compartment"))
Definitely it will work
Hope this info is help ful for you....