Wouldn't it be better to ask Toshiba? After all no matter what is happening here they have to support it if it is a Hardware problem or something relating to Vista.
What type of Disc are you inserting here a Program Disc to install something or some media Disc like Music or Video to listen to?
Vista has DRM Signing to protect Copyrighted Product like Music and Video if that is what is happening here you need to read the Users Manual or contact Toshiba for a workaround if there is one.
If you no longer have the manual you can download a copy from here
http://tinyurl.com/6fo66h
Col