SSD1306 OLED not working

 Was powering up my SSD1306 from an Arduino NANO with the SSD1306 display wired 5v - Vcc , gnd - gnd ,SLC - A5 ,SAD-A4 . It worked using the Arduino adafruit example in the Arduino IDE 1.8.15 showing the display as expected. I loaded a new sketch to my ide and it didn't work, didn't change anything. I reloaded the example and still no display, replaced the OLED and it worked. 
 My curiosity got to me so I decided to look further, there is a voltage regulator on the back of the unit (662K) which I determined that it is a 5v regulator with a 3.3 v output .I powered  up again and measured the voltage ,indeed 5v on center pin with respect to bottom left and 3v on lower right pin with respect to gnd also. I then checked to see if for some reason that the select link may be the issue and it showed 4.68K ohms so that is good. I then went and checked the D1 diode and it had 2.68v on diode test , reversed leads gave me .56v. Other than caps and resistors for the display , which I did not test can some one tell me what may be wrong with it. I know ,just simply replace the OLED but would like to know why this is happening,Thanks

OP text posted so that the text line wraps for readability.

Was powering up my SSD1306 from an Arduino NANO with the SSD1306 display wired 5v - Vcc , gnd - gnd ,SLC - A5 ,SAD-A4 . It worked using the Arduino adafruit example in the Arduino IDE 1.8.15 showing the display as expected. I loaded a new sketch to my ide and it didn't work, didn't change anything. I reloaded the example and still no display, replaced the OLED and it worked.
My curiosity got to me so I decided to look further, there is a voltage regulator on the back of the unit (662K) which I determined that it is a 5v regulator with a 3.3 v output .I powered up again and measured the voltage ,indeed 5v on center pin with respect to bottom left and 3v on lower right pin with respect to gnd also. I then checked to see if for some reason that the select link may be the issue and it showed 4.68K ohms so that is good. I then went and checked the D1 diode and it had 2.68v on diode test , reversed leads gave me .56v. Other than caps and resistors for the display , which I did not test can some one tell me what may be wrong with it. I know ,just simply replace the OLED but would like to know why this is happening,Thanks