Temporary freezing when opening video files

> I am running WinXP Pro SP-1, with Windows Media Player 9. The
> problem I have didn't always exist; it only began rearing its ugly
> head a couple of months ago, though I don't know exactly what brought
> it on.
>
> The problem is that whenever I open a video for the first time, the
> whole system freezes for about 5 seconds (to the extent that the mouse
> cursor won't move). After that, everything is fine--the video even
> plays correctly. Even stranger than that, if I close and reopen the
> same video file, the freeze won't happen a second time--unless I
> switch away, do other things, and open it again later.
>
> The problem doesn't happen with any other type of file; just video
> files. And the system runs great otherwise.
>
> This happens with MPG files, AVI files, and with various codecs (Intel
> Indeo, DivX, etc.). I've also tried third-party media players (Light
> Alloy, Media Player Classic, etc.), and the problem is exactly the
> same with all of them.
>
> I've tried different codecs (Nic's XviD build, Koepi's XviD build,
> various DivX versions, etc.), and I've even tried screwing around with
> ffdshow. None of these things has helped to eliminate this
> aggravating problem.
>
> Please help if you can...