Diagnosing Boot Failure. Suggestions Please.

I have various success booting up my desktop pc. Most of the time it will self reboot at the bios slash screen or during the memory test. When it does this reboot the screen remains black and does not attempt to post. Occasionally when I can get the OS to load it will freeze at the login screen. On the rarer occasions that I can actually login, it eventually self reboots or more often freezes with garbeled colors on one or more monitors (have 3).

I've attempted to update my drivers and firmware, but because I can't remain logged in long enough I haven't been able to complete some of the peripherials. I've updated all internal hardware drivers including mobo and gpu. To eliminate the peripherials, I've disconnected everything except the keyboard, mouse, and one dvi conection to a monitor. I've disconnected my hdd's to eliminate those.

I pulled the lower gpu (have 2 ati hd 4850's not in crossfire) and sound card, mainly so I could reset the cmos. Doing this enabled me to successfully login last night after three resets/self reboots. I left it running last night and found it had self rebooted to a black screen again this morning. Tried rebooting and that lead me to a windows update that became a garbled blue colored screen. Manual reboot went a black screen.

All cooling fans in the case, psu, gpu's, and heatsink are operating properly and I verified that case and proc temp are not the issue. Side panel has been removed, so definitely plenty of airflow. Early on in the issue, I used the Windows 7 DVD to perform a memory test which passed.

Alright, so after all that, does anyone have any ideas? Could the psu or mobo be dying? Could really use some help here. Thanks for your time!

_______________________________
-Mobo: GIGABYTE GA-X48-DS4, Rev 1.3, Bios F3B
-CPU: Core 2 Quad Q9450 @ 2.66GHz (not oc'd)
-Cooling: Thermalright Ultra-120 Extreme w/ Yate Loon 120mm & AS 5
-Mem: 4x2GB Corsair Dominator DDR2 1066 @ 5-5-5-15/dual channel mode (not oc'd)
-Mem: 4x2GB G Skill DDR2 1066 @ 5-5-5-15/dual channel mode (not oc'd)
-Video: 2x VisionTek ATI Radeon HD 4850 NOT in Crossfire (not oc'd)
-Sound: Creative Sound Blaster X-Fi Titanium Fatal1ty Pro
-HDD0 and HDD1: Seagate Barracuda 7200.11 500GB in Matrix RAID 0, striped 128kb
-HDD2 and HDD3: Seagate Barracuda 7200.11 500GB, storage
-HDD4: Seagate Barracuda 7200.10 750GB, storage
-Case/PSU: Antec 1200/Antec TPQ-850W
-OS: Windows 7 Home Premium SP1 64bit

Besides the 2 x 4850s, what are the rest of the system spec's?

Power supply, model and age ? How does the system run if you use a Linux Live-CD ?

Are you over clocked?

Sorry about that guys. My sig was turned off. Specs are below. PSU was purchased june 2008. Have never had any issue with it. System is not oc'd. Never got the time to do it. For shame. This issue just started Sunday. Thanks!

Have you tried testing the power supply?

What would be the best way to test the psu?

To test with another PSU instead. The memory config could be another potential problem.
What if you use only either one of the RAM sets @ 2x2GB. Do also run memtest 86+.
Are the recommended voltages for the corsair and gskill set same, check respective at their webpages?

mammut, I reseated the ram but I haven't tried running only one pair at a time. I'll give that a shot. I don't recall the recommended voltages, I'll have to check but I'm certain I set them and the timings based on the manufacturer recommendations. As I mentioned, I never got around to oc'ing the pc.

Try disconnecting / removing anything that's not required for a successful POST. So besides the CPU / HSF, 1 x DRAM module installed in the 1st DIMM slot, videocard, keyboard and mouse, and the 24-pin ATX and 4 or 8-pin EATX12V PSU connectors, remove all PCI / PCIe cards, and disconnect SSDs / HDDs and ODDs from the board. You might also want to check the voltages at the 24-pin ATX and 4-pin EATX12V connectors w/ a multimeter. If it still won't POST, remove the board from the case and connect only those components I made note of.

Redduc900, I'll give it a try. Thanks for the input.

I'm sorry if im actually no help, this thread reminded me of this image:

Idk how helpful/accurate it is/will be. but here!

Sorry I didn't respond earlier Kawzman, but I see Redduc got you the information you need. I recommend testing your ps using the instructions in those images. Here's a step-by-step guide for testing your PSU.

Hm. You said you had it started it up in the OS once, and it seemed to be working alright.. Self-booted over night, though.

So, I'll ask this.. Can you successfully get into your bios settings? Will it idle there indeffinitely?

It sounds like a powersupply issue - It's no longer giving out the juice it needs to to power your computer, so it's rebooting as a failsafe.

Thanks for the additional posts guys. Haven't had a chance to troubleshoot. I too suspect the psi.