I am experiencing lots of horizontal lines, changed the toner but still getting them?

If the print is a dismal gray rather than a sharp black, you are probably almost out of toner. This can manifest itself evenly across the entire page or in splotches or stripes, depending on the printer.
Sometimes you can wring a little bit more out of a toner cartridge by taking it out and gently shaking it from side to side (never up and down, as toner can spill out). You can also try turning up the printer’s contrast adjustment, if it has such a knob (usually on the back side if it exists). Faded print can also result from a dirty corona wire, because a dirty wire inhibits a full electrical charge from being passed.
If the printouts are consistently varied in density, and you have to frequently remove the toner cartridge and shake it to redistribute the toner inside it, make sure the printer is sitting on an even, flat surface.
Horizontal black lines
A horizontal black line on the printout is probably the result of a dirty or damaged roller. There are lots of rollers in the printer, and you can use the space between the lines on the page to determine which roller is causing the problem. Measure the distance between the errant black lines on the page and then use Table A to determine which part might be causing the problem. Table A
Distance between lines
Faulty part
0.5”
Registration assembly
1.5”
Upper registration roller
1.75”
Lower registration roller
2.0”
Toner cartridge developer roller
2.56”
Lower fusing assembly roller
3.16”
Upper fusing assembly roller
3.75”
Toner cartridge photo drum
Regularly spaced splotches
If there are evenly spaced black spots but they don’t extend all the way across the page, the problem is probably a scratch or flaw in the drum or a build-up of toner on the fusing roller. If the spots are less than three inches apart vertically, it’s probably the drum, because the drum has a larger diameter than the fusing roller.
Vertical black line on edge of page
This can indicate an almost empty or faulty toner cartridge or (less frequently) some spilled toner inside the printer.