You have an SP540V
It is an old machine - how many hours do you have on the scan motor. It may have reached its end of life - if not that then you have to check your servo board.
You need a peck or co-peck report to check the hours.
If you lost your scan limits you can reset the limits by doing the limits set up
You should bite the bullet and get a tech to look at your machine. What a tech might see is that the cable tension is off and it needs to be tighten. Or the servo board is malfunctioning. The tech would know what to do in service mode. We here do not teach users how to be techs.