Nano: not in sync error : avrdude: stk500_getsync(): not in sync: resp=0x00

After days of putting up this power supply board with everything soldered together. Now being happy and all after long working hours, I wrote a testing code for the board, and suddenly I got this error.

avrdude: stk500_getsync(): not in sync: resp=0x00

I know it means that my pc is not communicating with my arduino. but why? what is possibly the cause for this error?

I know it is not the problem from: 1, usb driver; 2, software; 3, the code; and I have not connected anything to pin tx, and rx.

there are my pin layout:
13 Sck
11 SI
Outpin 10: CS Digital Potentiometer enable Pin
Outpin 9: swtich P-fet (Power OutPut)
Outpin 8: swtich NPF (discharger)
A0: button OK (Digital)
A1: Button → (Digital)
A2: Button <+ (Digital)
A3: Shunt Voltage (Analog)
A4: Temp Sensor (Analog)
A5: Battery Voltage (Analog)
A6: Power out Voltage (Analog)
A7: Discharge Battery Voltage (Analog)
LiquidCrystal lcd(2,3,4,5,6,7);

test using USB-ttl, rx, tx. won’t work etiher

Sometimes happened to me, when connecting too many things to Arduino it lost synch. Disconnect everything and try to upkoad again. Whats your sketch size?

I got the same thing I suspect I may of accidentally blown or shorted something out as I connected components to it via a bread board. Think I've lost comms because of it, going to check mine @ work tomorrow. Check the power rails, make sure the crystals running etc. Is there a way of checking comms from the IDE as far as anyone knows??? I seem to be able to send stuff through the serial monitor but not sure if i'm getting anything back or not??Be nice to be able to echo something...

Rob493: I got the same thing I suspect I may of accidentally blown or shorted something out as I connected components to it via a bread board. Think I've lost comms because of it, going to check mine @ work tomorrow. Check the power rails, make sure the crystals running etc. Is there a way of checking comms from the IDE as far as anyone knows??? I seem to be able to send stuff through the serial monitor but not sure if i'm getting anything back or not??Be nice to be able to echo something...

I think mine is damaged by more than 40V input from the booster circuit to the analog input. I have trashed the board already.

mart256: Sometimes happened to me, when connecting too many things to Arduino it lost synch. Disconnect everything and try to upkoad again. Whats your sketch size?

the things are soldered to the board. there is no way to disconnect anything. but anyway, thanks for the tips