for some reason i can play half life 2 and any source based engine great but when i wanna play cs, half-life, or ns my fps drops from 100 in source to like 40 and when somebody drops a medpack or i look at a phasegate it drops to 10 fps. Can anyone help me?

Thanks.

What PC specs you've got? It is a known issue for some ppl(ati users mostly) that they suffer from fps-drops on some maps(metal) and near to PG, when medpack is dropped (flashes) and marine flashlight is on.