[Rajarshi Basu]"I have my HD footage on a USB drive, there are no speed issues. "
You should never use USB drives for video. Consider yourself lucky if you are not getting lots of dropped frames. USB delivers data in bursts unlike Firewire which delivers a steady stream. Bad for video work.
As for your "unrendered" labels....delete your thumbnail cache. It will automatically rebuild and should clear up the problem. Using the USB drive might be causing this thumbnail corruption, though not necessarily. Could be just a random occurance, which happens from time to time.
The reveal master clips problem usually means that the sequence was dragged in from another project...are you working on more than one system?