I tried absolutely everything for hours to connect to pc. Even HBOOT didn't connect. I thought it has to be the charging jack in my M7 that's faulty. Bought a new charge port flex off eBay and fitted it. Turns out that it was the problem .! The other symptom was a "Slow Charging" notification always came up even when connected to my HTC charger. That's what led me to believe the jack was faulty.