Boot device is unavailable

Hi,

On my Inspiron 15 3567, first Wi-fi adapter stopped. When I restart, pc hanged and when I powered it off and restart again, it when on support assistant pre-boot hardware check. It passed all check. After that during restart, the support assistant pre-boot screen appeared saying "Boot device is unavailable". Every time I tried to start, the same screen appeared. At the last resort I tried to press "Esc" on dell logo untill it start. And to my surprise it boot normally. But now the pc hangs between my works and when try to restart I get the "Boot device is unavailable" and only by hitting "Esc" repeatedly  on Dell logo I am able to start pc.

It happens only when it hangs and I powered off forcefully. When I shutdown and start the pc, it boots normally. The hardware check (Online and Offline) passes all tests. Please help to get rid off this thing.