First of all, the vertical lines on the screen.
Are they there all the time?
Look at the screen when you switch on the computer (before Windows starts). Can you see the vertical lines? If the answer is yes, the laptop probably needs a new screen. A more technical person can test this by connecting a screen from a normal (not laptop) computer to your laptop. If there are lines on the laptop screen but not on the normal screen then obviously the laptop screen has a problem.
It's amazing to have warranty on a 4-year laptop, so get it in for repair quick! If you don't have a warranty, a new screen is expensive, so you might as well buy a new laptop.
You say the only way you can switch it off is by unplugging it from the mains. This is strange because a laptop can get power from the mains of the battery. In other words, if it switches off when you unplug it this means the battery doesn't work. You need a new battery. The battery will not be covered by the warranty. A battery warranty might be 1 year.
Anyway, you don't have to unplug it to force it to switch off. You can hold down the power button, or hold the power slide switch in the other position, for about 10 seconds. It will switch off.
Basically computer problems are either "hardware" (the machine) and "software" (the programs and the Windows system). The screen and the battery are probably hardware problems, the freezing is probably a software problem. Once the hardware problems have been sorted out you the software problems can be sorted out by reinstalling Windows.
In any case, you probably have to send it for repair for the screen. If there is information you want to keep on the computer get someone to help you save it on a memory stick before you send away the laptop.