Have you read the wiki section on cheat codes, or the cheat codes text file that comes down automatically with torrent downloads? The wiki is found by following the Documentation link near the top of every forum page. What cheat codes have you tried?

While the above is the most likely fix, did you confirm a good download by checking the md5 (or sha1) checksum? Did you burn at low speed?

Mentioning just what hardware you are trying to boot on might allow more people to help you, particularly if this is a hardware issue that someone else with similar hardware has already resolved.