Sony Ericsson V630i won't start

[alekta]

Here is my problem. The other night I turned off my phone to change the battery and charge it (I have two batteries, one of them was empty so I wanted to charge it) and since then my phone doesn't want to start. I just get red light flashing when pressing the power button.
I have found a thread on this forum when someone had the same problem with the same phone - I wanted to reply there, but it was closed, here is the link: Sony Ericsson V630i wont turn on!!! - Top Sony Forums
Then I tried to download the upgrade program from official Sony Ericsson site, but it didn't work - I did all that it asked (fully charged the battery with another phone coz it says the battery has to be fully charged, I tried it with SIM card and without it, with memory card and without it), and when it said I had to press the C button, I did and hold it for a long time but nothing happened, so I couldn't go on because the computer didn't recognize that the phone was plugged in USB.
Any idea what should I do, is there any combination code that I could press and might help or something else I could do?
Any ideas and comments are welcome, thanks in advance for any help.