Strange & troubling behavor for 3 yr old Home built PC

I built my first PC a little more than 3 years ago:
Intel C2D E6750
Gigabyte GA-P35-DS3P motherboard
Corsair 620 HX PSU
4x 1 GB Patriot Extreme PC2-6400 memory
Evga Geforce 8800 GTS 320 MB Video card
WD 750 GB WD7500AAKS Hard Drive
CoolerMaster Hyper TX2 CPU cooler
Antec P180B Case
Microsoft Windows Vista Ultimate 32-bit
Westinghouse 22 inch LCD monitor

I did a few upgrades about 2 months ago:
Removed 8800 GTS 320 and added eVga GeForce GTX460 768MB
Added a primary boot drive - Samsung SpinPoint F3 HD502HJ 500GB SATA2 7200rpm 16MB Hard Drive
Kept the WD 750 GB HD as a data drive
Reinstalled Windows Vista Ultimate (but installed 64-bit version this time)
Changed the BIOS to to have the drive run in AHCI mode instead of IDE mode.
Added an eSATA bracket

Then about a couple weeks ago, I left my PC on for 3 days and on the 3rd day, my screensaver (which displays pictures) was on but was not cycling through pictures... it was stuck on one. And the screen saver did not turn off when I moved the mouse or pressed a key. I had to turn the PC off. Ever since then sometimes when I turn the PC on it turns on (fans on, lights on) but the monitor doesn't turn on and the PC does not boot. Sometime it freezes at the BIOS splash page. Sometime it boots into Windows fine. But occasionally it will freeze in Windows and require reboot. [Most of the time, once I get into Windows I'm good. It does not freeze often.]

I ran Memtest via boot CD and it froze the first time. On subsequent times, when it was able to finish one complete cycle, it said the memory was fine (no errors).

I also used a Samsung tool to check the Hard Drive via a boot CD, and it too would sometimes freeze. But when it completed, it said the diagnostics were successfully completed with no errors.

In Windows, I used HDTUNE and scanned the hard drive for errors and performed benchmarks and that all looked good. But at the bottom of the Info tab, it does not show all the same info for the Samsung HD as it does for the WD HD. Serial #, Buffer, Standard, Supported and Active are not populated for the Samsung HD like it is for the WD Hard drive. Also the Health tab is blank for the Samsung HD but is completed populated for the WD HD.

GPU-Z shows that the Bus Interface for my GTX460 768MB graphic card as "PCI-E x16 @ x8" so it appears that it is not using all 16 lanes.

Also, CPU-Z shows the Core Voltage as fluctuating between 1.168V, 1.184V, 1.2V and 1.312V and I don't recall that before - although maybe it’s a BIOS setting somewhere.

Any ideas what my problem could be? Motherboard? Memory? Hard Drive? PSU?

Thanks in advance for any troubleshooting tips or thoughts on my issues.
6 answers Last reply
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  1. Voltage fluctuation is likely due to speedstep. Are the voltage changes tied to the speed of the processor in CPUz?

    Also, if you have anything overclocked, put it back to default settings. If you have the old 8800, put that back in and try it to rule out the graphics card.

    Try booting with each memory stick individually. Try one, then the other, to see if one stick is bad even though it passed memtest.

    If it is stable when you boot into windows, try running prime95 to stress test the processor. If that causes an instant crash, you may have a bad CPU. Do you have another CPU you could try in the board?

    When you were installing the new hardware, did you ground yourself properly? did you bump anything like your CPU cooler that it might cause a crack in the motherboard? Did you drop a screwdriver on the motherboard (I've broken motherboards this way)?
  2. Memtest, which boots from CD, freezing...

    Remove all hardware or power connections you can spare (freeing up quite a few watts on a potentially aging PS), and retry....

    The video card alone could add 100-200 watts to your peak load (although rarely in 2d/virtually idle); a few big drives spinning up at the same time, might load down a weak PS....
  3. Reseat everything, including power cables, RAM, and the GPU. Check and replace your CMOS battery, resetting CMOS to defaults after you do this.
  4. I hate to say it but it could be due to your power supply being on its way out I would suggest that you substitute the power supply with a known good one to see if this cures the problem.
  5. Agreed, reseat all components. I'm gonna go with pjmelect and say this could easily be PSU-induced, but it could definitely also be a mobo failure. Check your caps, and see if any of them are leaking or bulging. I'm skeptical about a CPU failure, I don't see those happen too often unless you're OCing.
  6. Thanks everyone for your replies. I appreciate it. I'll try to get in there and reseat everything. I was suspecting the motherboard. I don't think it's a wattage issue - I think a have plenty of power. I bought the Corsair 620HX in order to have a quality PSU so I wouldn't have any tricky power issues. I hope that's not the problem.
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