Default [Q] Help I think i bricked my phone

I have a samsung galaxy s 4g from t-mobile I was trying to upgrade from ginger bread to ice cream sandwich and now the phone keeps restarting. When it turns on it shows the samsung galaxy s 4g startup then it shows the ice cream sandwich i tried to download and it shows a progress bar when it gets to the very end it restarts and does the same process over and over again. I tried to plug into computer and the computer says my device is not recognized. I need help!! What do I do?