stack in black screen with triangle and exclamation point inside and phone lying down

I tried to hard reset my karbonn A1+ phone by pressing and holding together volume down and power button but everytime i do it I got stuck in the black screen with triangle and exclamation point in it with a phone lying down. I tried pressing power button and volume up and down button but it has on effect. My karbonn A1+ phone has only 3 buttons which is power button and volume up and down button, my home menu is a touch screen button together with the back button. Please help me i want to format my phone since i can't open it because I forgot my password. I'll be much thankfull for your help.