Movement in slow-motion

Hello,

first of all, my computer specs:

Pentium IV 3,6 Ghz

1 GB RAM

Asus X800XT

I have a resolution set at 1600x1200. When I play the game (I'm at the beginning of the Peragus level), something strange happens:

The FPS and performance is good. But: when I walk (run) with my character, he gets slower and slower with every minute I walk, until my walking looks like slow-motion. Please note that the FPS (frames per second) is still great, only my characters movement animation is too slow. I hope you understand what I mean.

Please help. I tried everything like changing the resolution etc.

Thanks,

Frank