I bought and installed a 120GB Seagate HD and a Plextor CD/DVD/R today. I saw that the inside of my computer was very dirty and (carefully) unplugged and cleaned everything before the installation. I have a fairly old computer and most of the parts are 3-4 years old, except for the network card and the sound card, which I bought recently. My specs are: MSI KT3 Ultra mainboard AMD Athlon 1600 cpu 2x 256 DDR RAM Sound Blaster Audigy 2 soundcard Linksys Wireless Network card ASUS GeForce 3 vid card Pioneer DVD-ROM Plextor CD-R/DVD-R (just installed) 120 GB Seagate HD (just installed) 60 GB Maxtor HD (my boot drive) After I installed the new hardware, the computer would turn off by itself after 5-10 seconds, right as Windows is about to load. I tried fixing this problem for a long time and finally tried removing the little coin-shape battery. For whatever reason, this allowed my computer to run Windows until my desktop begins loading, and then it turns off by itself. Finally, I played around with the CMOS setup changing these 2 settings gives me a stable system: Disable Spread spectrum Set CPU FSB frequency to 100MHz The latter setting underclocks my CPU to 1.05GHz, whereas I ran it at 1.70GHz with no problem before I installed the new hard drive and burner. I tried changing the frequency to 133MHz; this causes it the computer to turn off about 5 seconds after booting. Then I tried 166MHz and this causes the computer to turn off by itself almost instantly. I had to use jumpers to reset CMOS to on both occasions to get booted. I'm typing this on a stable run now, and the new hard drive and burner are working fine. But, I'm at 1.05GHz instead of 1.7 This is not a heat problem, I don't think, because I checked the CPU temperatures and they are at ~50C, maxing out at 53C. I'm guessing this is a power supply problem, since I added a hard drive. My new burner also replaced a slower, malfunctioning, older one. A friend told me 300V should be all an old computer like mine needs and I have a 350V Enermax power supply, albeit one that's 3-4 years old. Should I get it replaced? Or maybe I damaged something while taking apart, cleaning, and putting together my computer. I'm fairly knowledgeable in assembling computers and I built my system myself, but can a static discharge or forgetting to plug something in cause these kind of problems? I would think it wouldn't even let my computer start up. I'm still running without my battery, by the way - putting in the battery again causes the computer to beep like crazy because it can't detect my video card. Any ideas what the hell is going on?