Sonia:
If the cable connection to the back of the monitor and from the monitor to the back of the computer are both secure, try this:
* Move any devices away from the monitor that may be causing interference (speakers, another monitor, a microwave oven, an air conditioner, a cell phone).
* Press the buttons on your monitor and select the degauss option (it will be a symbol that looks like a horse shoe with a diagonal line through it).
* Check that the refresh rate for your monitor is not set too high: Right-click on the Windows desktop and choose Properties. Select the Settings tab and click Advanced. Select the Monitor tab and choose a lower number (70 Hertz or lower) for the screen refresh rate. Select Apply, OK and OK.
* Have a tech savvy friend replace the video card or check for a conflict between the video card and the motherboard's onboard video controller. A recently added expansion card may also be conflicting with the video card, so have her try removing this as well.
* Or have her try downloading and installing the latest video card drivers as M_2 suggested.
Let us know if our suggestions don't do the trick.
Doc
