Hi Rashid1023v,
Your Mac might have forgotten where to start up from, or your data could be corrupted.
Try these steps:
- Shut down your Mac.
- Press and hold the Option key as you power on your Mac. Release the key when you can select a Wi-Fi network.
- If you see a startup disk appear (such as Macintosh HD), hold down the Control key. As you're holding it down, click the circular arrow that appears. This instructs your Mac to always start up from that drive.
If you don't see any startup disks appear, please let me know.