Hi, I'm trying to diagnose a home built PC running fine since 2007 but lately starting to act odd. Here are the system specs: Intel Core 2 Duo 1.8GHz cpu Asus P5B Deluxe mobo Nvidia 7900GS graphics card Kingston KHX6400 2x1GB DDR2 memory Sparkle ATX 400W power supply 3x 1TB SATA HDDs 1x SATA DVD-RW $ uname -a Linux spider 3.0.0-25-generic #41-Ubuntu SMP Mon Aug 13 17:58:59 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux $ cat /etc/*release DISTRIB_ID=Ubuntu DISTRIB_RELEASE=11.10 DISTRIB_CODENAME=oneiric DISTRIB_DESCRIPTION="Ubuntu 11.10" $ uname -a Linux spider 3.0.0-25-generic #41-Ubuntu SMP Mon Aug 13 17:58:59 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux What recently changed: i) replaced monitor, last one died ii) (carefully) vacuumed the dust from inside. Kept hand on case chassis, didn't touch any PCB/chips, etc. Here are the symptoms: 1) first started seeing BIOS claims of bad CMOS checksum at boot time. Immediately suspected the CMOS battery, replaced it and reset CMOS settings but I continue to see this. This is the one symptom that I can't yet place, unless it's simply a bad replacement battery. 2) next started seeing the monitor fail to wake up after entering power save 3) powering on the PC shows issues: 3a) often the monitor won't wake at boot 3b) the bios often doesn't finish POST, gets stuck at splash screen 3c) bios settings often don't survive across power cycles (possibly related to #1--battery issue?) 3d) bios doesn't always give the affirmative beep (likely same symptom as 3a, 3b) 3e) a cold power on or reset can take several "tries" before the system stays on. I.e. fans will spin up, then spin down, one to three times before staying on. When this happens it's pretty much guaranteed that it won't boot successfully. 4) system will freeze to user input while up. I.e. once I get Linux booted, as long as I disable monitor power save it will stay running for a while, but I observed it stopped responding to KB and mouse input earlier this morning. Here's what I've tried: a) reseated both DIMMs, reproduced issues; tried with just one DIMM, repro'd; tried other DIMM, repro'd b) reseated graphics card, repro'd; removed graphics card (now headless), repro'd problem 3e c) reseated CMOS battery (CR2032), repro'd d) pulled all non-essential cables and internal connections, including power and SATA cables from all drives, repro'd e) updated BIOS to latest version, repro'd Unfortunately I don't have another ATX power supply to try, but was thinking of buying one. I might also try an old PCI video card, but I suspect due to repro (b) above that it's not the cause. Anyone have any other insights or agree it sounds like a bad PS? I still can't explain symptom (1), will probably buy another battery to be sure. Five years seems like an old PC, but I'm not a gamer so this suits me fine. Thanks, Brett