OK So, I had this problem too.
My phone was not detected as MTP by the computer.
My phone didn't detect that it was attached to a PC.
On my PC --It didn't work.
Another PC --It didn't work.
Even another PC --It didn't work.
Mac --It didn't work.
Tried all sorts of things written on many websites. --It didn't work.
There was no MTP option in the status bar. It just always charged using the PC.
THEN... Finally 1 day, when I was looking at the back of my CPU (PC

) I saw my USB 3.0 Ports (the Blue ones). I had never connected anything to them. So,
Tried on a USB 3.0 Port --It WORKED!



My phone was immediately detected as MTP. The option showed up in the status bar. I could transfer files. But then- What about my USB 2.0 Ports?

Then I did the following :
Dialed *#7248# for the PhoneUtil options.
Under 'UART' tap MODEM. Under USB, PDA.
If this is already your setting, choose the another ones (PDA for UART and MODEM for USB) and then tap SAVE and RESET.
Again dial *#7248# for the PhoneUtil options.
Under 'UART' tap MODEM. Under USB, PDA. Finally tap SAVE and RESET.
Your phone will now be detected as MTP with all types of USB Ports now.
