Problems with USB-SERIAL comunication

Hi, I read a lot of post but I didn’t find anything useful in any of them.
When I try to upload I get a common error message: avrdude: stk500_getsync(): not in sync: resp=0xff (where I wrote ff every time I get a different number). I checked all the connections, used multiple usb cables, different PCs and OS, tried to press the reset button and the upload icon in different combinations of timing and the error is still there. Someone told me that the USB-SERIAL chip could be broke. What can I do? Thanks fo the help.

Is anything else connected to pins 0 or 1? That will often cause serial uploads to fail - remove those connections, pins 0 and 1 are needed for serial monitor and uploading sketches.

Do you have the right board selected? (tools -> board)

When you press reset on the board, does the LED blink a pattern of a few (3?) quick flashes? (that comes from the bootloader, to signal that it's running) When you upload to it, you should see that same pattern of blinks.

Yes, nothing is attached and I checked all the settings multiple times. And yes it blinks in the same way when I reset the board or I try to upload. But after I uploaded and the L led flashes the RX led flashes for some seconds (it flashes a couple times but it stays High for a very little time)