What message do you get in your browser when you try and go to the PIX? Are you definately using httpS://, not just http://? If you look at the config via your telnet session, do you see commands like:
http inside
If you do a "sho ver" from your telnet session, does the 2nd line show the PDM version you're running? Can you get to it from another PC? Are you sure you didn't upgrade your browser or Java version?