It was caused by the KVM switch you used did not pass the correct EDID of your monitor to Windows 7 system correctly.

To solve this problem
1). Add an EDID emulator between connected system and the existing KVM switch or
2) Find new KVM switch support Full-time ALL EDID/DDC.


Here are some suggestions, if you want to find a new KVM switch:

When select /upgrade new KVM switches for Windows 7 systems, the following important criteria should be included.

1. To avoid video resolution changing when selecting to/from Windows 7 systems,
make sure the KVM support Full-time EDID/DDC communication or called "Dynamic EDID mapping".

2. To avoid USB HID devices (keyboard, mouse or touch screen..etc) repeatedly mounting and dismounting when slecting to/from connected Windows 7 systems, make sure the KVM support USB DDM (Dynamic Devices Mapping).

3. Supporting of Special/functions keys of connected keyboard and mouse, make sure the USB DDM technology is on the spec.