i cant upload programs

Dont know what happens and im going crazy.

Im new in arduino word, i bought a new arduino duemilanove complatible board. When it arrived i tested it with "blink" sketch, and it worked correctly. two days later i was using it again and it stoping working, now i cant upload programs to the board. When i try to record the programs it start to upload but when process is 90% completed, the loading bar, stops and gets frozzen. And dont know why, if it worked correctly why dont work today?

I have tryed in other computer and doesent work too, so i think its a board problem, but dont know what to do. some help?

when process is 90% completed, the loading bar, stops and gets frozzen

Does it give any error after that?

Do you have anything at all connected to the board, when you upload, apart from the USB cable?