Arduino upload problem

i cant upload to my arduino ti says

avrdude: stk500_getsync(): not in sync: resp=0x30
avrdude: stk500_disable(): protocol error, expect=0x14, resp=0x51

What type of board? (Deumillanove, UNO, MEGA)?
Are you sure you selected the right serial port and board in the IDE?
Is this a Arduino out the box or did it just start doing this?
Do the RX and TX lights do anything such as always off, always on or blinking?

And what operating system do you use? (eg. Windows XP, Ubuntu, mac, exc.)

Thanks for the replays but i had to change the serial port and now it works XD