SD Card removed unexpectedly

Hi,

I use a htc desire 816g since feb 2015.My phone worked very well from Feb till May.

One afternoon, i was using both WI-FI and mobile data and was quickly shifting from one to the other to test a process speed. Suddenly my phone got hanged.

I switched it off to restart but it did not start till 5-7 minutes. When I opened the Flip cover, it took a minute and then turned on.

Since then whenever I turn off my mobile data or WI-FI, I get a modification "SD Card Unmounted Unexpectedly".

I gave it to the store where I bought it, he suggested to reboot it. So he did and gave it back to me. Still I am getting this problem.

Please help, I want my phone to work like it use to before. W#waiting for a fruitful reply.