Since you don't state the model number of your tablet, this may not be of any use.
If you have a HDMI port on the tablet, connect the tablet via the appropriate HDMI cable to a TV (or monitor) with a HDMI input and see what its display is like. If the display is good it is a fair chance that only the screen (and possibly the touch facility) of the tablet is faulty.
If the external screen display only displays lines as well there is most probably a systemboard problem and maybe a screen problem as well.
If the external screen is OK, try pressing on the tablet screen and see if the touch facility works, (you'll probably have to guess a little but at least the external screen will let you know what's happening). If the touch is not working, try plugging in a USB mouse (if there is a USB port on the tablet) and see if you can navigate using that.
After all this at least you can determine what is working and what is not.
Hopefully this is of some help.