Brother HL 1440 Laser printer-horizontal black streaks

Three Horizontal lines indicates a 'Light Burnt Drum'. The drum units are light sensitive. If they are left in the light too long they will be affected and it will show as black horizontal bars. The number of bars really depends on the circumference of the drum some are 2 some are 3 some can be 5 etc.

Solving this you can only replace the drum unit. Check with your local remanufacturing outlet to source a replacement drum unit at a price WAY better than buying new.

What software are you printing from? It sounds more likely to be software causing the issue.

sounds like a possible problem with possibly the drum or the transfer belt. trying a different toner cartridge may fix the problem but it may not. Most likely given the cost of repair, replacement may be your best option.
thank you,
Lee

The first thing I would try is to fix the corona wire. Here is a link to Brother's website outlining the process (clean corona wire).
What you need to do is pull out the drum and look for a blue tab on the top of the cartridge. Slide that tab back and forth along the wire and see if that clears things up.
I have had some luck cleaning the drum when I get black streaks but I have also hear this can be dangerous and make the problem worse.
http://welcome.solutions.brother.com/BSC/public/us/ca/en/faq/faq/000000/000200/000008/faq000208_022.html?reg=us&c=ca&lang=en&prod=mfc7340_us_as&Cat=7

Download your Printer Drivers:
http://download.cnet.com/Brother-HL-1440-series/3000-2116_4-72913.html
Install them to your Computer, verify if it works!!!

If you're experiencing horizontal streaks, and already tried changing cartridges but that don't help, look in the bottom of the paper tray. If that small metal ground terminal gets ditry or bent, that could be the cause.

may some dust in corona ware or drum clean the drum.

Seems like the drum needs changing. This is the most common cause for print problems in these printers. If using the high yield TN 6600 toner then you need to change the drum every 3-4 toners. If using the low yield TN 6300 toner then the drum will need replacing every 6-7 toners. Hope this helps

Did you mean 'vertical' (from top to bottom) line rather than horizontal? If it goes 'straight down,' it has to be. I think so, otherwise the added info that it is closer to the right wouldn't make sense.
This problem is normally due to contaminents on the surface of the drum itself although can also occur if a wire that discharges the excess toner from blank areas could be dirty.
Changing the drum cartridge will correct either of those problems since they are contained in the drum cartridge. If you are using 'recharged' cartridges and it only has a few copies on it, most companies will exchange it for you.  
 

try the fuse in the plug