The ONLY way to reflash your system is to flash it using the phone built-in flasher.
As already mentioned put the update.app in a 'dload' folder in the root directory of your SD card. Turn off your phone and press Power+Volume up+Volume Down simultaneously. I did that already more then 3 times and it's working perfect!
This will start the flash operation immediately. After its done your phone should work like before.
because the internet over here is pretty slow, takes about 4 hours to download the rom...