Q. I am editing a large video file, and every now and then, my screen goes black and the computer seems to lock up. Is there anything I can do to prevent this?

A. It would appear that you are exceeding the capabilities of your video card and/or the memory available to it. When there is not enough memory to display everything, the screen will either freeze up or turn black or possibly blue.

The best solution would be to install a video card with greater capabilities and more memory. If you are going to be editing videos frequently, I would suggest that you get a computer with sufficient video and other hardware capabilities suited specifically for this purpose. Video requirements are quite high for video editing.

However, there may be something you can try to alleviate the problem or at least make it more possible to use your current hardware. If you reduce the screen resolution and/or the color depth it may help. To reduce the resolution or color depth, right click the desktop, and choose Properties, then the Settings tab. (On Vista you Right click the desktop, choose Personalize, and then Display settings).

There you can change the resolution and Color quality. If the resolution is set to 1024 X 768, a common default resolution or non-wide screen displays, you can try lowering it. (The most common default resolutions for a wide screen would probably be something like 1280 X 800).This will force you to display much less of the picture on the screen at one time and may require a lot of scrolling, but will definitely use less video memory.

You can also lower the color depth, and this may be preferable so I would try it first. If it is set to 32 bit, try lowering it to 16 bit. There will probably me no detectible difference in the picture quality with this reduction. If available, you might also try reducing it further to 256 colors (8 bit) The picture will not look as good, but there will be more memory available to display the video.

Here's why lowering the resolution or color depth will require less memory.

8 bit color depth has 256 distinct colors and takes 1 byte of memory to display the color of each pixel. If your resolution is set to 1024 X 768, there are 786,432 pixels on the screen. (1024 times 768). At one byte per pixel, to display the color alone requires 786,432 bytes (.75 MB) of video memory,

16 bit color depth has 1,572,864 distinct colors and takes 2 bytes of memory to display the color of each pixel. If your resolution is set to 1024 X 768, there are 786,432 pixels on the screen. At two byte per pixel, to display the color alone requires 1,572,864 bytes (1.5 MB) of video memory,

32 bit color depth has 3,145,728 distinct colors, and takes 4 bytes of memory to display each pixel.. This is usually the default setting. If your resolution is set to 1024 X 768, there are 786,432 pixels on the screen. At four byte per pixel, to display the color alone requires 3,145,728 bytes (3 MB) of video memory.

So, although this will probably produce a less than desirable quality picture, lowering the resolution to 800 X 600 and the color depth to 256, you now have 480,000 pixels, requiring only .45 MB of memory to display the color. This will allocate more memory to do the actual editing.

So, reducing your resolution and/or color depth will reduce the amount of RAM needed to display the screen. This may allow you to edit the video without the problems mentioned heretofore.