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Because this is a older machine and the video card that is inside is conflicting with this external VGA device, What I recommend is purchasing a internal video card PCI e and installing that. The new video card should have dual monitor support so make sure you ask for that.
I am sorry that this did not work for you plus you said the other one you had, is doing almost the same thing witch confirms its a conflict with the primary video card.
Solution purchase a internal video card with dual monitor support for the work around.
Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/edwy_1a56970cf1ea4620