iiyama X2483HSU factory reset
Solution 1:
tl;dr;
Press the AUTO button for 2 seconds. Then select the input of your choice.
monitor reference
iiyama 24" LED ProLite XB2483HSU-B1 - 1920 x 1080 pixels - 4 ms - Format large 16/9 - Dalle AMVA+ - Pivot - HDMI - haut-parleurs - Noir
what I understand so far
From the moment I connect an HDMI input, the automatically selected input will always be HDMI. So if I plug a VGA input I got the "No signal detected!" message.
By pressing the AUTO button for 2 seconds, you can go back to manual input selection and choose VGA (D-sub) again.
See John Tetmaier answers.
Solution 2:
In the same situation, I've press the "Auto" button for 6 or 8 sg untill came on screen a little orange menu where you choose the entry method. My screen : iiyama ProLite B2712HDS.