Help Screen Issue

[phrozenwire]

Have a Micromax A78. Its having a wierd issue. Whenever I make a call or receive a call my screen goes off which may be because of the proximity or light sensor but then when the call is disconnected, the screen doesnt come up again and it doesnt activate even after pressing the power button. The phone has to be hard rebooted to start the screen again. Mailed the Micromax support group and they asked me to do a format and re-install which was done and the phone was OK for a couple of days. Again the problem cropped up. The only solution to it is a reboot. Please assist.