if your computer crashed and you lost settings, you can restore to the last backup (MT makes a backup whenever it starts). To do that, just start MT, go to FILE / IMPORT… Select BACKUP folder, and then select the most recent backup before the problem started.
one line is for the start of session. The other is for start of day. You cannot get rid of them, though you can create a custom chart color set and specify the grid color to be the same as the background. Then just select that custom color set on the chart.