I have a Sony Xperia SP C5302, untouched Android 4.1.2 (12.0.A.2.254)
Last day I rebooted the device and it didn't turn on, and I haven't installed anything, just normal use. I tried several things and I could turn it on first with the reset hole on the back (10 seconds), then pressing volume down + power, and the device turned on ok. Later I realize the pc (with PC Companion) doesn't recognize the phone. It's the same pc I always use without issues, and with the original cable. Tried on a different pc, but it's the same, luckily I can charge the phone without problem.
Today I made the factory reset, and the only good thing I got is that now I don't need to do the 10 seconds on the back hole, but I must press volume down + power to turn it on, in fact if I just press power (and not volume down), it vibrates but it doesn't turn on, and it won't turn on again unless I do the 10 seconds on the back. The PC still doesn't recognize the phone.
If it helps, phone was rooted and I was using GravityBox for some tweaks, but it was like that for quite a long time, without any issue.
I'd really appreciate your help!