Hi, I'm having a problem. I've tried everything I know of or could find in a couple days of searching. Since installing a new power supply & video card, my PC is having frequent slowdowns. The mouse will freeze for a few seconds and then teleport across the screen, typing text (like this post) will have occasional freezes and then catch up, etc. In online gaming (City of Heroes) the video will stutter. Also, the sound stutters, both in the game and when playing system sounds and MP3s. Ingame, the sound and video both stutter at the same time. My first thought was heat, so I installed a program called RivaTuner to let me see the video card temperature. It hovers around 36-37 degrees celsius when web browsing, and has risen as high as 44 degrees while gaming. I haven't gamed for more than two consecutive hours yet, so it may go even higher. That said, the fans seem to be doing a good job of removing the heat, and the problems are about the same regardless of temperature. According to what I've read, for a video card anything under 60 degrees is good. I opened the device manager and uninstalled the old video card driver. There were no hardware conflicts and DMA was not disabled. DirectX is updated to 9.0. Drivers: the new video card came with a CD that installed nv4_disp.dll, which Windows XP says is unsigned. On the off chance the card didn't come with the latest driver, I downloaded the most recent one I could find from the MSI website, but it was the same. The audio driver is also unsigned, but it always has been and it hasn't been a problem before. Tried updating that, downloaded a generic A4.06 from Realtek, sound problem got worse. I then tried the latest available for my motherboard at the manufacturer's website (A3.62), with no change. I also checked the motherboard manufacturer's website for any updated chipset drivers (one of the suggestions I got from searching these forums), but there wasn't anything new listed for my motherboard. System info: OS: Windows XP Professional Version 2002, Service Pack 3 Motherboard: ASRock 939Dual-SATA2 Processor: AMD Athlon 64 3700+ 2.2GHz RAM: 2GB Kingston ValueRAM 184-Pin DDR 400 New Video Card: MSI N9600GT 512MB PCI Express 2.0 x16 Old Video Card: MSI NX6600 256MB AGP 4X/8X New Power Supply: CORSAIR CMPSU-550VX 550W ATX12V Old Power Supply: FSP Group FSP400-60THN-R 400W ATX 2.0 Audio: RealTEK AC97 Audio, ALi M5455 Nothing is overclocked. The new card is in a PCIe 1.0 x16 slot, but they're supposed to be backward compatible, so in theory I should just not be getting the full performance. Thanks in advance for any help. Marian EDIT: I've just discovered that both the video and audio drivers are now signed. Must've happened when I downloaded the latest ones. EDIT: While doing another search, I came across the claim that stuttering is almost always due to CPU activity. I ran a couple of tests, and I think this may be the problem. What I did was open the Windows Task Manager and click on the performance tab, then launch City of Heroes. The CPU usage instantly shot up to 100%. I logged in and played a little bit, and the usage mostly stayed above 96%, occasionally dipping, but the lowest it ever got was 77%. I then closed CoH, opened Winamp, and played an MP3. The CPU usage ranged from 0 to 21%, and the audio stutter always coincided with an increase. This gives me some new keywords to search with, so maybe I'll find the answer on my own. But if anyone knows what might be causing this, I'd sure appreciate any help.