Hi AlanHo - Welcome to w7forums
Do you have the most recent windows 7 build? 7600 is the most recent. 7229 is the build I am currently using.
Are you sure you have a copy of Windows 7 downloaded that has not been tampered with. There is a MD5 Checker that you can use to check your download. This is always a good thing to do when downloading files from the internet if your download has a MD5 hash code.
Are you sure you got a good DVD burn. There is always a chance of burning a bad copy especially if you burn at the max speed.