Nano avrdude

Hi guys,
i was working on my arduino project to school and everythink was working. Then i changed few cables and arduino won´t upload my code.

This is what i get every time i try it to uplouded.
avrdude: verification error, first mismatch at byte 0x0000
0xff != 0x0c
avrdude: verification error; content mismatch
avrdude: verification error; content mismatch

Do you know what to do to fix it?

If you disconnect all external wiring, circuitry, and components from your Nano, does the problem still occur?

Yes it does.

Sometimes re-burning the Bootloader will fix that problem. Maybe you could find someone, classmate/instructor, who could help you re-burn the Bootoader? You would need either an ISP programmer or an Arduino used as "Arduino as ISP" to do this.