Mount SD Card failed. What now?

[AC Question]

Hello, i have a HTC Desire 600, and recently it displeys an icon of a red triangle above a phone on a black background. If i leave it like this, it keeps restarting itself over and over again. I read somewhere that i can press volume up and the power button, then select reboot system. But it doesn't change a thing.

Can anyone help me?
Thanks