Why does my phone not respond after double tapping?

When my phone is on and it sits idle for some time (maybe a couple of hours), when I go to double tap the screen (near the center of the screen), my phone doesn't respond. I have to use the power button to turn it on. Also when turning it on with the power button it goes immediately off again.
This goes on a couple of times before I have to do a complete reboot by holding down the power button for more than 5 seconds. Can you help?

Welcome to Android Central.

Try a Cache Partition wipe.

Also - and I'm not sure that this would in fact be relevant - are you using an SD card, which if bad, may be causing problems?

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