I have an old VGA monitor (Xerox XM7-19w which has its prime resolution as 1440x900 (i.e. WXGA) at 60Hz. I've connected my recently purchased Pi 3 (and recently purchased sdcard with Rasbian on it) using a PiHut hdmi to vga converter without using the audio out as the monitor has no built in speakers and I only have usb speakers. Only my mouse & keyboard are connected by usb (directly to the Pi) and my internet is connected by ethernet cable.
Booting up is Ok (whether I have the monitor switched on before booting or after booting to Raspbian GUI). The monitor displays Ok but goes blank when I move the mouse. I can get the display on by powering it on and off but it happens again when I move the mouse. I've successfully installed Raspbian from the above mentioned sdcard and upgraded the software Ok, with lots of monitor switching off & on.
I've tried adding to the config.txt (just containing hdmi_force_hotplug=1) e.g. hdmi_ignore_edid=oxa5000080, hdi_drive=2, hdmi_group=2, hdmi_mode=47. But still no improvement.