well title says it. sometimes when im playing on a map and alt tab out of the game the game crashes, and i mean a full system freeze. so far it seems not consistent. im using nQuake v1.7a and afaik that includes ezquake 1.9 alpha (build 1985? ). is this a known problem?bad cfg setting somewhere (only changed stuff in menus)? or is my pc simply fucked ?

windows xp
pentium 4 3.2 ghz
nvidia geforce fx 5700 ve