Why is my smart cover sensor not working?

I did try a hard reboot, and the smart cover.

I did not try a software restore because I do believe that deletes all the data off of the ipad and I am working on this ipad for someone and did not want to lose there data. but if that is my last resort then I may have to try it.

Is there a way to back up there data so I can try a software restore?

when I try the hard reset I hold the home button and power button in after it is turned off.

the apple symbol appears then is gone, then reappears and I let go. does this sound correct?

You should press & hold Home and Power Button together for at least 7 seconds. I hold them together for 12 seconds. If the device does not restart, I release both and just click on the Power Button. I do believe a software restore is a last resort, since a simple reboot should be enough in this case.

The PMV cable connects to the side board and is covered by a piece of foam. Make absolutely sure the connecter is very tightly seated and the piece of foam is properly inserted and squeezing/holding the connector in place!

If this does not help, try examining the 2 tips of the thick cable that connects the main logic board and the small side board; then the 2 connectors where the cable sits on the 2 boards; also examine the area on the 2 boards around the connectors (in fact, examine the boards wherever there are apparent components): may be you knocked off a component or damaged the cable or connectors in some way.

If you did, post an image of the damaged/missing components.

To back-up, I open a new user on my laptop (I use a Mac). That's important because if you use iTunes with your own Apps already on it, once the iPad is restored some of the Apps may transfer to the client's iPad using your Apple ID & pass which will be needed to update the Apps later on - or he'll have to delete & re-install them.

Ideally, I ask for client's Apple ID & password if they trust me with them & use them to authorize this temp user & to log into iTunes store using iTunes. This allows to transfer all Apps & content & music to my computer during back-up. Without ID & pass, the back-up will only transfer photos & contacts.

Then I do an "encrypted back-up" (don't forget the password!). After 1st back-up is finished, I click a 2nd time on back-up & this time get prompted to "back-up apps" which I accept. For safety, I click on back-up a 3rd time. To restore, I prefer to do it from DFU mode. Once all is restored/verified, delete the back-up file from iTunes>Preferences>Devices & sign out of iTunes Store.

Thank you very much for the suggestions. I posted a picture at the top, do to not knowing how to post one with this comment. I do not see anything wrong.. I am going to try and back up the device the way you said to and do a software restore and see if this resolves the issue.