Power Macintosh 7500 & 8500: Vertical Lines Follow Cursor

I have a Power Macintosh 7500 series computer, and I have recently noticed that two vertical lines appear to be following the cursor. What could cause this, and how can I resolve it?

Two vertical lines following the cursor or vertical lines all over the screen are symptoms of improper installation of VRAM on Power Macintosh 7500 and 8500 series computers. If you have 2 MB of VRAM installed, you must install the VRAM DIMMs into the slots labeled 1. For example:

1 ________________ 1 MB VRAM DIMM
2 ________________
1 ________________ 1 MB VRAM DIMM
2 ________________

Also, you cannot install 3 MB of VRAM. The Power Macintosh 7500 and 8500 series computer allow only 2 and 4 MB VRAM configurations.
Published Date: Feb 19, 2012