Member Avatar for WireDog69

OK, I read the pinned post and that didn't help so, here goes:

I acquired a CPU from a local retailer, it was the display model and had been placed into the back room after they changed their setup. While it was in the back room, someone had removed the side panel and the RAM module. But, I figured for $20 it was worth it even if all I could salvage was the case. It came with no cords, no manual, no anything except the CPU. I brought it home and didn't really deal with it until a few weeks ago when I had the time. I installed a DDR RAM module (128 MB), plugged a cord in (got plenty of those), hooked up the keyboard, monitor and mouse, and pushed the button. The fans spun for about 3 cycles, like it was starting up and then nothing. Fans stopped and the monitor never flickered even once. I replaced the PSU and the problem remains, it is like something is internally shutting it down as soon as it is turned on. Now, being reasonably intelligent in the ways of Electronics, I would normally assume this points to a "dead short" somewhere but, my knowledge of power distribution within a PC is not as good as within an FM Radio. I would love to be able to build from the basic's of this computer as the Motherboard is not that bad (I researched the specs). I am hoping that this problem doesn't point to a bad Motherboard. Can anyone tell me where to look to find the base problem? The "Computer Repairmen" in my area are crooks, they sold my friend a rebuilt laptop for $400 that had an intermittent problem with the display and refused to repair it within the warranty period and then wanted to charge her $200 afterward.

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Short expert note to supplement the thread: correctly narrowed the likely culprits to CPU or motherboard, but a few targeted checks will often identify the fault without buying parts at random. The following sequence is inexpensive, safe for someone comfortable with basic electronics, and built to eliminate chassis/connector/BIOS issues before replacing core components.

  • Breadboard the board outside the case with the minimum required parts: PSU (24-pin + CPU 4/8-pin connected), CPU with heatsink, one known-good RAM stick in the correct slot, and video if the board needs it. Power the system and observe behavior.
  • Verify the front-panel power switch and wiring by momentarily shorting the two power-switch pins on the front-panel header (use a screwdriver or jumper) to rule out a bad case switch.
  • Visually inspect the motherboard for bulging/leaking capacitors, burn marks, or damaged traces. Check the CPU socket area for bent pins or thermal compound contamination.
  • Clear CMOS (remove the battery for a few minutes or use the clear-jumper) and try again; attach a PC speaker if possible to catch beep codes, then look up the BIOS vendor’s codes.
  • If still no change, measure PSU rails and 5VSB with a multimeter to confirm the PSU actually delivers stable voltages under load (this verifies the replacement PSU and rules out shorted rails). Also check for motherboard shorts to the case (missing standoffs or misplaced screws).

When a definitive test is needed, a cheap known-good compatible CPU or motherboard (not necessarily new) is the fastest confirmatory step; swapping both at once makes diagnosis impossible. Take static precautions, reapply thermal paste correctly, and remember some OEM boards may require specific BIOS versions for certain CPUs. These checks will avoid most unnecessary purchases and make the final replacement choice much clearer for a salvaged Pavilion like the one and are working on.

Member Avatar for Mike.Rigsby

In my experience that behavior is generally caused by a blown motherboard, bad ram, or a bad processor. Can't narrow it down much but if it was ram you'd probably get beep codes when you turned it on and the fan would still spin. If I had to pick one, I'd say a failed processor.

Member Avatar for WireDog69

OK, I know the RAM is good because it is currently working quite well in my other desktop. So that leaves the Processor and the MB. My options are:
1. Buy a processor (about $13 at ) and hope for the best. If this fails I will know it is the MB and will have to get one of those for around $50. But, I will be sure that the problem is the MB.
2. Replace the MB with a combo (about $60) and still not know which component caused the problem.

Decisions, decisions. Is there a possibility of it being any other component? Not that I mind spending the money for a new MB/Processor but, I would really hate it if I did and the problem was still there.

Member Avatar for Mike.Rigsby

No, I can't think of any other component that would cause that problem. You've already done a good job of troubleshooting out possibilities, such as a bad power supply and the ram.
So I think it is highly likely that it's either the processor or the motherboard but failures in either could cause that problem so I can't give you a definite answer.

Member Avatar for WireDog69

OK, I have a MB and processor on their way, plus the thermal grease and anti-static strap (Mama didn't raise no fools here), a new DDR2 RAM module plus a new PSU and case fan for my other Desktop that I have been meaning to get. I guess the bottom line is, if the MB isn't bad, I can always order a second processor and drop it and the new MB into my other Desktop that is in DIRE need of a major upgrade. Either way, I will update you as soon as they arrive and I know what is up. Maybe I'll end up with 2 upgraded Desktops after I am through.

Member Avatar for TwentyGauge

What did you find out about your machine? -- I just picked one up off the side of the road that does the same thing.

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