At this point, I would recommend pulling all the carts and the print heads. Try powering up and see if you can get the printer to ask for the ink carts. If you can get to that point, after which it will ask for the print heads, you may be ok. If it won't power on and gives a 3:10 error immediately with all the carts and print heads removed, could be you have a bad or incorrect MAIN PCA board. Actually, once you start switching out components one by one rather than just getting a new PSU all in one go, you can find yourself in no man's land.
In my experience, sometimes replacing some of the previous components can work if in fact they are still good. Obviously, you know that if your printer is an "A" Rev, everything must be A.... not B, etc.
If it's still giving you the 3:10 error, then it stands to reason you haven't solved the original 3:10 issue. Hate to state the obvious or what seems like the obvious, but retrace your steps again. See if there are any pinched wires anywhere. There is a red and black cable that runs from the Main PCA board to the print mech board, and it powers the scan axis motor. Sometimes that cable can get pinched when putting the end cap back on. It's worth a check.
Usually you can dig deeper into the error code by pressing the on, up arrow and menu switch simultaneously (if I remember) and the error code will go into a further explanation. Try that when it comes up next, and if it doesn't work, scour the manual to find out which button combination gives you the info.
Insert words of encouragement here - been there done that - keep going, I guess. :-)
Mark
