Just power it normally and check all of the power rails with a multimeter, i.e. check that you can see the +5V rail and that the 3.3V VDD/VDDA/VDDC look correct. Try using only bus power coming from USB rather than the barrel jack if that's what you've been using.
If there's not an obvious electrical problem there, put it into DFU mode like you would for rescue and make sure that it's showing up as a DFU device with your operating system. On Linux that can be done with
lsusb for example.
If that all checks out then go back to trying rescue mode in the patcher, does the app actually report that it connects to the device and then start trying to flash?