Lines show across my camera when I take a picture

Go to the menus and reset to default or factory settings. Make sure that the white setting in the picture adjustments in the menus are set to zero or you may have to adjust + or - to get the normal effect again.
Test the camera by taking pictures and saving to a sd card. Then put the card in a card reader/writer which is connected to the computer. Copy the pictures or files to the computer and view them to see if they are in good shape or if there is some problem with exposure or the way it looks.
If the computer pictures show that they are good, and they are not showing good on the camera LCD, then the LCD has a problem, and is possibly either cracked or has some other display problem.
These LCD screens are not that hard to change if you are good at working with small items and screws. If you do this, make sure you have a way to remember where you got each screw, as they can vary in size and kind.

test

Is your camera getting overheated in the sun?

keep iso 100 and set ur screen brightness

For both of you, this sounds like it might be a defective CCD imager. If so, Canon should fix this for you for free, including free shipping both ways. This is regardless of your camera's warranty status. Please check the following two links for more info:

http://camerarepair.blogspot.com/2007/11/canon-digital-cameras-showing-black.html

http://www.usa.canon.com/consumer/controller?act=PgComSmModDisplayAct&fcategoryid=225&modelid=13390&keycode=2112&id=29819

Applicable cameras include:
A40, A60, A70, A75, A80, A85, A95, A300, A310, S1 IS, S60, S200, S230, S330, S400, S410, S500, SD100, SD110, IXUS V2/300/400/430/500, IXY Digital 200a/300a/400/450/500

Hmmm... your batteries ok? i had this recently and changed my NMHI batterys and cured it...

It's the CCD in the camera. You can take into a repair shop and see if it can be replaced.

This sounds like it might be a defective CCD imager. If so, Canon should fix this for you for free, including free shipping both ways. This is regardless of your camera's warranty status. Please check the following two links for more info:

http://camerarepair.blogspot.com/2007/11/canon-digital-cameras-showing-black.html

http://www.usa.canon.com/consumer/controller?act=PgComSmModDisplayAct&fcategoryid=225&modelid=13390&keycode=2112&id=29819

Applicable cameras include:
A40, A60, A70, A75, A80, A85, A95, A300, A310, S1 IS, S60, S200, S230, S330, S400, S410, S500, SD100, SD110, IXUS V2/300/400/430/500, IXY Digital 200a/300a/400/450/500

Two things can cause lines across the LCD either horizontal or vertically. The first (and most likely) is a small crack in the display wafer. LCD stands for Liquid Cristal Display. They are very fragile and can be easily damaged if dropped. I broke one in my pants pocket.

The second would be if a pin on the ribbon cable (to the LDC wafer) was not making good contact. If you disassemble the camera it is possible to clean the contacts using contact cleaner (or alcohol). Only attempt this is you are willing to replace the camera if you don’t put it back together properly.

I have the same problem too with my a430, when i shoot outdoor, it's like over exposed, more of a white, but it's good indoor shooting aside for some horizontal lines. i already reset all the settings, still nothing changed