What is rstech_teni on a ematic 7 HD quad core it says it stopped

Rstech_teni is in your tablet as a core system app even though it may be no such thing. I believe it was put there by the tablet manufacturer in some contractual agreement with some advertising entity. The Lookout malware scanner may sometimes detect it as malware you should just ignore it and not try to delete it, as it will result in your problem again.
You will not be able restore the tablet from the hardware restore menu (hold power & up vol) because it will not allow you to answer "yes" to the prompt to proceed.

Two ways to fix, (Later, on how to actually select something)
1. (preferred)
Go to >Settings >Apps >All
scroll down to rstech_teni, select it, and then select "Clear data"
If you don't see retech_teni you may find "rs_9104_v30". This may be a clone of rstech_teni, do the same to it.
Your done.

2. (last resort, you will lose installed apps and data)
Go to >Settings >Backup & reset >Factory data reset,
Follow instructions, and your done.

And now the hard part, to deal with the message that will not let you navigate.
The easy way to get to "Settings" is to short tap power button to put tablet to display off/locked.
Then again short tap to turn on screen. You will see the rstecc_teni MSG hit OK in MSG. The MSG should be gone and not come back, do nothing else other than pull down the right upper drop down menu where the settings button is then select settings. At this point the evil MSG will come back.
From here on the frustration will start.
You will need to use two hands. Tap the rstech_teni OK with one finger on one hand and then quickly tap the Apps option with a finger on your other hand. This is kind of time consuming but it works after multiple attempts.
If you have a stylus pen, use it for the second tap to the option you want. It will seriously reduce the time it takes by making the second tap very accurate.
Within a half hour you should be able to get through this.
I know because I had the same problem.