Problem with the serial monitor and generally board!! pls help

I have a problem with a plate Arduino UNO with ATmega328 microcontroller, and I do not know if it’s 8U or 16U but I was using my arduino normally when i upload a simple code while i open the monitor serial at the same time, then it show me a strange error. I tried to upload again the same code but now show other error like this:
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_getsync(): timeout communicating with programmer

And until then it has been so, the arduino have uploaded the last code before than first error, I have not been able to upload a diferent code, i need all posible solutions plss…
PD: Sorry for my english, it isnt my native language :smiley: