Monitor suddenly acting weird

My current monitor is a Dell 15" flat screen that I've had for a little over 13 years (got it in June 2000). Then a few days ago after my system has been on about a half an hour, it started showing horizontal black and white thin lines that slowly moved down the screen, then returned to normal video. About an hour later the same thing happened, but it didn't go away. I turned off the power to the monitor and when I turned it on again, the screen was just a gray mottled appearance. I disconnected it from the desktop CPU and tried it without being connected. When I turned it on and off several times and it either showed the lines, the gray screen or a combination, then finally it looked normal. I tried an old CRT monitor with my computer and it worked fine and the flat screen worked fine with an old desktop I have that runs Windows 98. I re-connected the flat screen to my current system and it worked fine for two days. Today when I turned on the system, the gray mottled screen was present again with about an inch wide purple band at the top. I turned it on and off a few times until it looked normal again. Below is a screen shot of my internal hardware. What could the problem be?

 

Cable usually, they go bad more often than expected so wiggle the cable around see if you can get the errors back, it would definitely explain the intermittent fault.

If the cable is built into the monitor then your out of luck, 13 years is definitely value for money though so give it a good funeral.