If you have a spare partition you could try doing a fresh install of the OS + P96 - see if that works.
Also, try running Picasso96prefs to make sure it still recognises the Pixel64.
Obvious things:
Try lower resolutions and 8-bit modes.
Check all the cables and everything are still secure - including the -12V wire.
Try removing and replacing the Pixel64 card.
Are the ateo libraries still present in libs: ?
Check there isn't a loose screw under the busboard shorting out connectors.
Is the "c:startateobus" NOREBOOT command still in your startup sequence?
I know they're obvious things, but it never hurts to double check.
Regards
Rich