Screen won't light up during a call

This is a recent problem, but whenever a call comes through, the moment I answer it, even if I haven't held it to my ear, the screen goes dark. If I pull the phone away from my ear during a call, the screen won't turn on, so I can't turn the phone on speaker or access an application during a phone call. Only when I end the call does the screen come back. I've tried holding a light to the screen during a call to get the sensor to turn the screen on, but that doesn't work either. What's happening and how can I fix it?

Have you tried hitting the  button to get the screen to come on? You can also just hit the $ key which is your speaker button.

Hit what button? Sorry I don't think my computer recognized the symbol. But thank you letting me know about the $, I'll remember that.

Just push the touchpad and the screen will come on.