156 Radio Code query

[silverman166]

2005 156 1.9 Jtdm, duff alternator flattened battery, radio code not accepted after CODE and four dashes, code entered within 20secs, get WAIT. It times out, then try again, but code still not accepted. I believe I've used the code successfully before, but can't be sure. Before removing radio to establish S/No, is there any other way to sort this out, please?

Various posts have suggested leaving the radio on for 1 hour, then entering the code before switching ignition off - would this apply even after the normal procedure above has been tried? If so, why?

Something's also been mentioned about resetting ECU - would this apply in this case?

Not 100% sure how to remove the radio if I need to - there are small holes at each corner of the radio unit into which I understand some form of stiff wire should be inserted, but how long should this be and should it have a hook on the end? Is the idea to use two of these wires together at one side in order to release the latches, then pull the unit out slightly at that side to keep it unlatched while the opposite pair are worked on in the same way? Or is there another technique?

(Have posted this on 156 Tech forum, was advised therein to try here - hope someone can help!)