Vista Media Center working VERY slow

HeyI've been running vista ultimate for some months now, but in the last few weeks i have experienced a major step down in performance and speed of media center, it just lacks all the time, even when only using 20% of CPU power. when i restart media center it works fine until i enter a function from the "startmenu" like recorded tv, or musiclibrary. after that, no matter how long i wait, it just lacks, the menus function as always, and if you have some knowledge to MC then you can move through the menus "in the background", but somehow it seems that the images or UI is just not keeping up.Any ideas? help is much appreciated. Please forgive my english, I'm danish... :)SRJ