CrAzY: What OS are you using? If it's XP or 2000, press Ctrl+Alt+Del, go to the Processes tab, and try to figure out a rough average of the CPU Usage (at the bottom). Also, (still just 2000/XP) do this, which will copy a list of processes running to a text file so we can check for viruses:
1. Start -> Run -> cmd.exe
2. Type "tasklist /svc >> c:processes.txt"
3. Open c:processes.txt and paste it in a post.
Of course, if you're using '98 or non-Windows then that's all completely useless.
You could also reinstall/update
DirectX if it's only 3D stuff that's affected, and update your graphics card drivers.
SilentGunz: trojans are a
family of virus, there are hundreds, probably thousands of them, not just the one.