The last banner will not roll back to the first one

I try to make a web to let more guys find us easily.
But there is something wrong with the slider.

I made a banner, and suddenly the last banner will not roll back to the first one.
And when roll to the last banner, you can not do anything with the banner, even you click it and try to move back or move forward.

Could someone can help me with this problem?
The web is https://polyresingifts.com

Thank you very much
Leo