Why my tablet screen goes off and on. it will not stay on completely

Do an Android Soft Reset.

Power Off
Press and Hold the Power button and the Volume Up button until you see the Recovery Console.

You can choose Reboot or Factory Reset.

PBS Kids Playtime Pad 7" Kid Safe Tablet Multi PBSKD12B

https://www.bestbuy.com > ... > Tablets > All Tablets
The PBS KIDS Playtime Pad (PBSKD12B) is a full-featured 7" kid-safe tablet that reinforces fun, interactive learning experiences. It comes with more than 25 ...

Reset Videos

https://www.google.com/search?q=PBS+kids+tablet+reset

..

https://www.youtube.com/watch?v=yWr8MIN3eJo

Solution #1: Power Cycling/Restart The Device
Simply Turn OFF the Android phone and tablet completely. To restart device with touch screen not working: Press and Hold Power button until your screen goes black. After 1 or 2 minute, press and hold the power button to switch ON the device again.
https://www.androiddata-recovery.com/blog/resolve-touch-screen-not-working-problems-on-android

Try a factory reset of your tablet first. Here is a link to the procedure:
http://www.rcatablets.com/how-completely-reset-your-rca-android-42-tablet

If it doesn't stay on , you may have a broken battery . If you're out of warranty, somebody has to open the device and replace the logic board. The part is available on ebay. On youtube you will find a guide on how to disassemble an Insignia tablet. Maybe a tech savy friend can do it for you. If you want to pay to have somebody do it for you there are third party Insigina Repair Services.

go to display settings and set the black light lcd time

Have you done a factory reset?

3 RESET WAYS on ANDROID TABLETS REVIEW

MaybeMay

Replace it with a new LCD Inverter, you can address the following issues:
Screen image, but the power light stays in
Dark display, but still readable
Flashing on and off of the screen between 1/2 to several seconds
The power indicator stays on, but no display and sound
Screen images, but LCD TV still has sound
Picture cycle on and off, as well as high-power LED lights
More information in: http://lcdinverter.info

hardware issue i think