Unplayable after 2-3 arena games, with getting more and more spikey game

Hi,

i can run any game on the highest quality and got 1gb internet. All drivers updated and deleted all addons.

My game keeps getting more and more spikey. the only way to remove it is to reboot my pc ( restarting game doenst work ).
then the game works fine for 15m, playing arena / doing bg's seems to decrease the playable time.
i upgraded the .exe to allow more than 2gb to ram, no result.
i googled the perfect settings, disabling specular lightning, fullscreen glow effect, deatheffect, textures all now all, you name it.

i have no idea how to solve this.