Iphone 4 shuts down and stuck on logo when on power

Iphone 4, IOS 6,
factory unlocked, never jailbroken, not under waranty anymore


Few days ago, the phone just went off. It did not fall down, it was in my pocket.
It was not reacting to power button and it could not be turned on.

When connected to USB, the phone goes to apple logo, then again shuts down. This repeats and gets stuck on the logo. Otherwise, if not connected to USB, the phone is off.
When put in the restore DFU mode, itunes gives error 2001 (like it is problem with the cable)
After a while, I managed to restore it.
Then, the phone turns on normaly. And it is functioning normaly. Everything on the phone works perfectly when it is on- Wifi, camera, network, battery charging....

Then, again after few hours it shuts down, and it is not reacting. Same problem appears when connected to USB. Goes back to logo, and it is difficult to put it out of logo mode.
If disconnected from USB charger, it shuts down immidiatelly.

If in that state, I hit the phone on the flat surface, it turns on and working normally again.

I would suppose that it is some hardware issue inside, might be a cable, connector or something else. Really do not know, this is a guess.
Would appreciate any input/ help on what might be causing this

thanks