I'm having a similar issue with an ATI x800. I've been playing CS:Source on this rig for more than 2 years without a hiccup at the highest graphics settings available and rarely had fps below 90. Typically run windowed at 1600x1200 on an NEC FP2141SB CRT. My fps typically ranged from 90 to 200 (P4 3.6GHz, 2Gb DDR2 RAM, 7200rpm HD on an Alienware laptop).

About 3 weeks ago something happened with CS:Source. I join a game and everything is good for about 30 seconds, then I get a stuttering sound, the graphics card spins down like there isn't a load on it at all and my fps goes from >90 to less than 30 and stays there.

I've removed Steam and all local content for CS:Source - reinstalled fresh after doing a serious cleanup and defrag of the hard disk. I updated the ATI drivers to latest edition for the x800 Mobility, I've even tweaked lower DirectX versions (forced 8 and 8.1), set heapsize to half my RAM, set affinity to only one processor since it is HT - all to no avail. I did the SANDRA comparison as suggested but don't know exactly which memory benchmark you're referring to - please advise.

This has to have something to do with a Source update because I haven't changed a program or a piece of hardware (it is a laptop). It is really driving me crazy for some CSS goodness...any help would be greatly appreciated.

Maybe ur video card has finally come to the end of its life?

Certainly could have, although everything else runs just fine, so I wouldn't expect it to be a EOL issue...

I've had exactly the same problem with my CS:S. I've been playing with this machine for a year now, it has an x600 PRO graphics card and I've never had a problem. I come to play the game again after a few month break and I get so low fps.

I join the game i get 100fps easy, a few rounds in and my FPS drops to <30 and wehn i go to shoot someone my fps drops to 15-18. I've tried a fresh install of my whole computer, installed omega drivers, reinstalled the latest catalyst, reduced my res to 800x600 in game and even set every graphic setting to low in game.

Im trying to find out the problem, though I'm saving for a gfx card anyway, but until then I want my fps back =[

CSS woes

The mystery goes on. Why would a program that has worked for years suddenly become unstable and now not run at all. Every “cure” that I have found has done nothing for me, every possible component has updated drivers. I installed a different GPU, albeit older tech it should still handle CSS.
However there is a new twist, I noticed that my clock was off by over an hour, I reset it but after a few days it was off again. It would seem that my CMOS battery was the most likely culprit. After changing it and resetting the clock it still runs erratically, losing time, although not at a constant rate. Is it possible that my chipset may be damaged? I had thought about flashing my BIOS but that could be a fatal mistake if the chip is going belly up. What do you think?

Please make a new thread on the topic... don't hijack someone else's thread for your purposes.