we have a problem with our old MXProDV and when its turned on it just shows a blank screen and all the lights are lit on the board. Tried factory reset to no avail.
Check this page ( videonics.com/dynassets/documents/downloads/MXPro%20Video%20Mixer.pdf ) though it may not solve your issue. As it did not solve mine.
This might be a bad question, but have you tried applying the negative effect to see if that does anything. With ours, I had a short near the transition button. Maybe you've got a short near the "negative" effect button that causes it to come on. You could try removing the button to see if that stopped it.
If it's in warranty, try to get it fixed that way.