sounds like you're just missing a ROM on your phone. Can't you just download the ROM you want, put it on your SD card and flash that to get back up and running? Or restore a NANDroid backup?
...assuming you mean you rooted your phone and then failed at flashing a ROM..but it sounds like you might mean you attempted to download and OTA update after being rooted?
Download a ROM, put it on your SD card, boot into Recovery (vol. down + power), wipe all data, cache, dalvik, then install the new ROM from the SD card.