Hi,
Kindly test if the mic is working fine using Windows settings -> Sound Settings

If there's no input, you may need to update your soundcard driver.
If mic is fine, kindly check WavePad Options (CTRL + SHIFT + O), Recording Tab if recording device is selected

If problem still exist.. Without closing WavePad, try closing the current file tab, and open a new one

Sync between WavePad and Mic might still be busy in that file tab.
Hope it helps.