Ive had the same issue with my DL4 and have done the same troubleshooting. Factory reset does nothing at all, it still does not power on.
Im curious to know if it worked for 'jistraminclowre'..?
But what else is there to do? Can anyone direct us to someone/somewhere Line 6 to get this issue fixed or get a DL4 replaced?
This seems to be a very common issue with the DL4 with no real response or support from Line 6. Which at this point should be addressed easily
and quickly considering how many people have the same, similar, or other issues.
Any other help would be appreciated.