Tethering USB and Portable Hotspot not working

[Sir1969]

Hello everyone, i'm trying to use my Xperia U as a router for my pc, as i need it when i'm not home, but i'm having some trouble. It won't connect to the internet even though data connection works fine. The Pc connects fine to my smartphone but it doesn't reach the internet. An error message pops up saying "thetering connection failed" either with the hotspot either with the usb tethering. The internet provider shouldn't be a problem becouse tethering worked fine with the previous smartphone.

Android version is 4.0.4, build is 6.1.1.B.1.89, the latest one. Any help would be appreciated.

[Uliwooly]

What if you install PCC on your PC?

[Sir1969]

Already done that, it's installed and i have used it to update to last build..

[Uliwooly]

Is your phone network branded/locked to a carrier?

[Sir1969]

Yes it is, but the SIM card is now different from the original carrier since i have changed contract

[Uliwooly]

it could be a carrier/network restriction. 

[Sir1969]

Do you think it could be solved by flashing the phone?

[Uliwooly]

It could be, you could flash the global generic firmware and check again 

[Sir1969]

I'm trying to flash the generic firmware and i'm using Sony Mobile Flasher. I have already recived the unlock code for the bootloader (it's a more than two years old second-handed phone, so no worries about the warranty), but i'm having trouble entering flashmode. I have installed the drivers via Flash-tool drivers.exe (flashmode, fastboot and xperia U drivers) and the next step should be pressing BLU on FlashTool, hold the volume (-) button while connecting the phone and somthing should happen (like inserting the unlock code). But after a few seconds the green light has turned on, it than goes in recharge mode and nothing happens (same thing holding volume (+), the fastboot blue light turns on for a few seconds than it goes recharge mode). I have even tried to enter in superuser mode, but yet again nothing happens. It really looks like it's impoosible to applay any changes to this cellphone (even though entering #*#CODE#*# gave positive response for what concernes fastboot unlocking). Do you have any idea?