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Have two computers, 98 and XP, toggled together with the one flat screen Dell monitor. All was working well until I mistakenly changed the hertz value on XP. Now I can use 98 and see the screen OK, but when I try to access XP to see that windows screen - all is blank except for the message - signal is out of range. I can hear windows XP loading but no picture so cannot access any program to try to do anything.
Can anyone suggest what I might do to fix this problem or is it going to take a tech to come in to do something?

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