Every time I want to swap out CD's in my PC's DVD drive, it still thinks the old disk is in there - complete with directory tree and everything.

The only way I can get it to recognize a new CD is to reboot the whole machine, which is mighty annoying.

I've tried everything I can think of to fix it, but am at a loss. Any suggestions?

System is WinXP Pro, on a Medion 2.66GHZ machine. DVD drive manufacturer is unknown.