Lag on certain Steam games

[The Monkey]

So since I got my computer back about a week ago, certain games have began to lag.

I don't have a huge number of games installed, but I tried most of them, and this is the result.

Normal performance (35-50 fps):
GTA: SA
HL2: DM
CS: S
Ricochet

Subpar performance (5-15 fps):
TF2
L4D2
Portal

It made little difference in these three games if the graphics was set to normal or to the lowest. The three poor-performing games all run on the same version of source engine (I think), so the problem might lie there. I've validated the files for all three games without result.

Any ideas what the cause of this is and/or suggestions how to fix it?

 

[Dekstar]

Got your computer back from where, and what had changed since last time you played those games (hardware upgrade, Windows reinstall, etc)?

 

[Vegeta897]

The normal performance games you listed have markedly lower system requirements than the subpar performance games... you know that right?

 

[The Monkey]

The normal performance games you listed have markedly lower system requirements than the subpar performance games... you know that right?

Yeah, I know, that's what I'm worried about.

Got your computer back from where, and what had changed since last time you played those games (hardware upgrade, Windows reinstall, etc)?

Two things got changed, I got a new network card and a a new graphics card. Neither of these should matter, though, as my internet speed wasn't decreased with the new network card (in fact it increased about fourfold), and they simply replaced my old graphics card with a new one of the same model (ATI Redeon HD 3400 Series). So I don't really see how these changes could've impacted on the performance, but then again, I tend to be wrong in these matters.

 

[Acepilotf14]

The GPU might be flawed somehow, if it changed performance dramatically just from replacing it.

 

[Hectic Glenn]

Are you sure it is the exact same model of GPU? Either your drivers aren't installed properly or your GPU isn't as good.

This is one of the reasons I'd always rather fix these things myself than send them back to people to fix. God knows what they do...they just rip people off with 2nd hand parts most of the time.

edit: Does your card have the PCI-E power connector on it?

 

[The Monkey]

You need to dumb the language to simian levels. What is the PCI-E power connector and how do I know if it has it?

Also, it seems like I have two GPUs installed. Now, when the monitor cable is plugged in at a different outlet, it shows as NVIDIA GeForce 7100 / NVIDIA nForce 6200. This is the one I have been trying to play with before, so I'll try to connect with the other one again, but that has proved problematic in the past, as the monitor rarely connects in that outlet. Ah, well, I'll try it.

 

[Acepilotf14]

Look inside your case at the graphics card, is there a wire plugged into it?

 

[Hectic Glenn]

You need to dumb the language to simian levels. What is the PCI-E power connector and how do I know if it has it?

Also, it seems like I have two GPUs installed. Now, when the monitor cable is plugged in at a different outlet, it shows as NVIDIA GeForce 7100 / NVIDIA nForce 6200. This is the one I have been trying to play with before, so I'll try to connect with the other one again, but that has proved problematic in the past, as the monitor rarely connects in that outlet. Ah, well, I'll try it.

I have no idea what this means, this is very very strange. Can you take a picture of the back of your PC? And a picture of the inside with the side panel off?

As a PC gamer, I would suggest you do a little bit of reading around what is inside a computer so you are able to to interpret problems to other people with better clarity. It will help a lot in the future.