CANT upload sketched----arduino UNO---avrdude: stk500_getsync() error...

i had a Arduino Uno it got ruined so i went and got an otherone. but this one doesn't upload sketches!!!!!. i did everything again install the drivers and all. before the arduino was on comn3 now its on com4 i know that shoudlnt make a diff. i have tried pressing the reset button restarting the program and reconnecting the board...nothing works. the program recognizes the port (com4) and the right board (uno) is selected...what am i doing wrong.. didnt have this problem beofore!!:(..pls help

error msg: avrdude: stk500_getsync(): not in sync: resp=0x00 avrdude: stk500_disable(): protocol error, expect=0x14,resp=0x51 cheers SN

Consult the installation & troubleshooting forum.