I've barely used my Speedlite 430EX II, but now I can't get it to fire with my Canon 7D while on-camera. I've tried disabling silent shooting mode, but that didn't help. I've also tried changing the flash mode (to manual and back to ETTL), the camera mode (I tried M, Av, P and full auto), and I've looked through the entire menu of the camera without finding any issue or relevant setting (the flash settings are all defaults). The device is communicating, because I do see it in the external flash function settings menu. The test button does nothing. There is no complaint about the batteries. The camera is communicating with the flash, I'm careful when mounting it, and neither is visibly dirty, so I can only assume full contact. The test button does not work when the flash is off camera either. There appears to be no slave mode setting that I can find, only ETTL and manual. I cannot find a wireless menu item related to external flash.
If the Test button does not work, this is a sign of internal issues, or batteries. If the Test button is not lighting up in red, then the batteries are bad, not fully charged or there is an connection issue in the battery bay. If the Test button is lighting red but pressing does nothing, then there is an internal issue with your flash, and you should contact Canon.
The Slave mode would be indicated on the LCD, as it is enabled via the Mode button.