Vertical coloured lines, started with one, now there are over 25. This is an IMac computer.

Maybe the video card. Try to spray with electronic contact cleaner the connections (pc cable to monitor).

This is typically a bad or loose cable to the monitor inside the computer. While you can open the iMac, Apple doesn't make it easy. It requires special tools, and there is a lot of tape involved. You can go to an Apple store to get it fixed, or to most computer repair places. It will likely cost you a little more than doing it yourself, but if something gets messed up in the process, they will be on the hook for fixing it, while if you did it yourself, now you have two things to repair.

How long is a piece of string? is the kind of question you've asked. I've a sneaking suspicion you'll get sick and tired of it before it finally goes.

interface cable or video card memory problems

Your laptop screen has been faulty. you can checked it from service center.

Your computer needs a new LCD.

normally the 19" resolution can support up to 1280*1024, but if it comes with vertical lines in full screen, it might indicate the panel is no longer to work and probably it's time to replace new one.

Most LCD monitors have a default refresh rate of 60 Hz. Older monitors also have limited resolution. Please check your display settings and ensure you're not using a refresh rate higher than 60, or a resolution higher than what it supports. If either one is the case, you're lucky the LCD still works.

Attach an external monitor (you may need to buy an adapter to try this) and turn on Display Mirroring in the Display preferences.
If the same symptom shows on the external monitor, then you've got a video card problem. If not, I'd say you're screen has some kind of damage of failure.
Sorry, but either one is likely going to require a trip to the Apple Hospital.
At least with the display problem, you could use the external monitor until repaired.

uninstall video driver reboot it should start on windows basic video drivers if it does and screen is good try reinstalling your original card drivers. or search on the net for updated ones