Old sketch is not wiped

I’m quite new here and already ran into the first trouble…
I have an Arduino compatible Nano with the 328 chip, running on Linux (Ubuntu 14.04). I tried variations of the “Blink” example and everything was fine. After every variation I did a new upload and the new example ran.

Now I have connected the power-, GND-, SCL_, and SDA-pin to a pressure sensor and then I put the USB connector into the board. On the sensor there was no power connection. Now there is no upload possible, even after disconnectiong the sensor device. I hit the reset button after or before the upload, or when powering up the board - no difference…

The error messages are:
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x00
avrdude: usbdev_open(): did not find any USB device “usb”

/dev/ttyUSB0 is present, as told by ls

lsusb gives:
richard@neuer:~$ lsusb
Bus 001 Device 031: ID 0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC
So the Arduino is seen by the PC.

Did I possibly kill the board because of connecting it to an unpowered sensor?

Thanks for helping - Richard

SCL,SDA have nothing to do with the Serial lines. Don’t see why that would have mattered.
Did you try the loopback test to see if the USB/serial chip is working?

Thanks for pointing me to the loopback test. Everything I type appears in the terminal window (Gtkterm) and the two left LEDs of the board flash with every keystroke. But the solution of my problem was so simple that I blush telling this: today I connected the board to a diiferent USB port and everything was fine... Richard

That happens sometimes. Bad cable, flaky port.