I just bought Doom3 some weeks ago to play with my kids here at home. Have it working flawlessly on 2 PCs. But the 3rd PC, which is the fastest has severe performance problems. Oh, please - help! Symptom: While running the game, FPS drops down to like 2-3 for about 15-20 seconds, then something clears up and FPS goes up to 40-60, but only for a few seconds, then drops back down to 203 FPS. Cycle continues endlessly. It's better when I set all advance options to no or off, and set the game video down to the lowest resolution. But, even crunched down to the worst game settings the game menu allows, it's unplayable. These stall periods happen every 10-15 seconds and last 10-15 seconds. You can't even get up the stairs without wanting to throw the monitor out the window. PC is a reasonable box, I've built myself: ASUS M2N-MX SE motherboard AMD Athlon64 X2 3.01Ghz 6000+ CPU 2GB PC6400 DDR2 RAM ATI Radeon HD2400 PCI Express x16 graphics card with 256MB DDR2 vram WD VelociRaptor 300GB 10Krpm SATAII HD OS: Windows XP SP3 DirectX 9.0c All recent updates and patches loaded and installed. Doom3: Patched to 1.3.1 System Options: Low Quality 640 x 480 All Advance Options set to NO or OFF ATI Video Drivers: I've installed the latest drivers and ATI Catalyst software from AMD web site: Driver Packaging Version 8.95 Catalyst Version: 12.3 2D Driver Version: 220.127.116.1156 Direct 3D Version: 6.14.10.0894 OpenGL Version: 18.104.22.16854 ...I have tried setting all 3D settings down to performance. No help. I've reset all 3D and catalyst settings back to factor default, which is pretty much "Balanced" (half way between performance and quality). DoomConfig.cfg definitely reflects finding 256MB video ram, so the game is detecting the video card's abilities correctly, to some extent. dxdiag finds nothing wrong. I have studied the Doom3 tweaks for hours. I've tried tinkering with the anisotropic and anti-aliasing settings but I can't seem to make a difference. I am so frustrated, I could scream. I found on some web site help for my older PC using an ATI Radeon 7500 (All-In-Wonder) card. The game was un-playable until I found this trick to set: seta r_useVertexBuffers "0" seta image_usenormalcompression "1" ...that was magic. The game plays great. I'm hoping someone has had a similar (frustrating) experience as I am dealing with - and knows the magic fix. Please help.