Loop Back Test

i done all that, and when i writed few characters in serial monitor and entered is dose not apeared what i writed, but the arduino TX and RX had blinked 1 time every time when i typed something and entered,
Pls reply me fast i need to know what is going on with my arduino, i chouse everithing corect but all the time when i try to upload that error apears : avrdude: stk500_getsync(): not in sync: resp=0x00
and the red (L) Led all the time blink fast, like 3 or 4 times per sec, when i try to upload the RX led blink few times and again the same with the red light.

Maybe wrong board selected ...
What arduino did you have?
Have you set it properly in Tools -> Board -> choose your arduino board
Also did you have the right Serial port selected?