Unplayable due to lags

[Myxir]

Hey!
Yesterday I returned from a one-week trip. This morning (yesterday's night aswell) I wanted to play Regnum but it is quite unplayable. I am running through the landscape and I get heavy lags. I don't know if this is a problem with my pc or the game or the server.
Since the update which disabled the shaders for ATI the game went very fine. But when i returned yesterday i had massive lags.
When i walk around i always get set back many steps. Even with Mobility at level 4 and wild spirit at 5 i cannot catch a conjurer. After the lag my char turns into another direction aswell. I did not press any key.
My Settings are:
Anisotropic filter: 1x
Antialiasing: 1x
Terrain Detail: Off
Terrain Quality: Very Low
Water Quality: Low
Texture Quality: high
View Distance: low (before it went very good at ultra high)
checked boxes are: Weather FXs, Lightning and Particle FXs.
As I already said before the trip it worked perfectly. CPU usage is at ~85-93% and FPS are 30-42 depends on where i am. I play without sound and music. During the lags the fps counter shows me 0-9 fps.
I cannot imagine that this problem is only caused by my computer, but it's possible, though.
AMD Athlon 64 3000+ (@1,8 GHz)
ATI Radeon X550XT
2 GB DDR-Ram
Anyone experienced this too? The game is unplayable for me now...