If DiskAid does not seem to be able to connect to your iPhone, iPad or iPod touch, make sure your device and computer are connected to the same WLAN/LAN network. Cellular Network (3G/4G) can sometimes take over the Wi-Fi connection. This prevents DiskAid from connecting via Wi-Fi. To avoid this issue you can alternatively connect your device to a power source or turn off Cellular Data in your device "Settings / Cellular".
If the above still not solve connection issues follow those steps:
If your device has a 3G/4G connection, go to "Settings / Cellular" and turn "Cellular Data" off and on. Try again to connect with DiskAid.
If it still doesn't work press the "Home" button on your device to verify that Wi-Fi icon is displayed on the top status bar. At this stage the device usually appears in DiskAid.
If still no luck, open DiskAid preferences and click "Restart Mobile Services", it solves most issues.
Reboot (totally powering off) both your computer and the device and try again
If it still not working make sure all system updates have been applied, proceed to any applicable system update
Check that you are running the very latest version of both DiskAid and iTunes and upgrade if applicable
Reboot once again (totally powering off) both your computer and the device.
Every single step is crucial, don't skip any one of them. You might be giving it a try after each single action.