I have three computers hooked up to the same monitor via KVM switch. on a Windows 7 desktop, the monitor says "1280x1024" is acceptable but on the other two computers (both XP) it says "no signal" if I climb above 1024x768! they were all set to "1280x1024" to begin with and I had to Google how to lower it because of the issue. why can one computer be set higher than the others all of a sudden? and what do I need to do to get them back to all 1280x1024?