Problem with LG Optimus screen

[oldbean]

I have an LG Optimus M (not sure whether it's the same thing). Every time I try to make a phone call my screen will go black and none of the buttons will work. Even if i try to hold the power button to just turn it off, it won't work and I have to take out the battery to shut off my phone. I'd tried restoring it to factory settings which didn't make a difference. Is there anything I can do to try to fix this or do I just need a new phone?

If it matters, besides phone calls, everything else works just fine.

Any help is appreciated!