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About four years ago I built this system:

Biostar TForce4 AM2 motherboard 
AMD Athlon 64 3800+ @ 2.2GHz 
2x512MB Corsair CM2X512A-6400 DDR2 
ATI Radeon X1800XT (512MB RAM with dual outputs) 
Antec SP-500 Power supply 
Seagate 80Gig SATA 

It worked beautifully for about two years. One day it suddenly would not power on. It's exhibiting symptoms of a short (when you press power, comes on for 1/2 second) but I can't find a short. I removed everything but graphics, RAM and CPU, and no go. I even took the board out of the case and it did the same thing...could this symptom be a result of failed RAM? I'm thinking if I just replace the RAM it might start...Should I try new RAM or something else? I don't want to pay $70 for a service call if possible.

Thanks

Edit - 10/28/2010

Ok it was my power supply. I learned that a "dead" PSU can show the same symptoms as a short. Too bad I didn't figure that out for so long--it actually stopped working two years ago (within warranty period). Just didn't have time to dig in to the problem until now. Anyway, I am going with a Corsair this time which has a 5 year warranty. We'll see...

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Have you tried replacing the power supply? –  ricbax Oct 24 '10 at 17:12
    
No need for the "[SOLVED]" here. –  Arjan Oct 28 '10 at 20:35

3 Answers 3

up vote 1 down vote accepted

When it doesn't beep, try for 2 times to power the machine on without cable attached, this is a PSU reset. If it still doesn't work, try another PSU (in 95% of cases you are now done). Then remove anything from the mainboard besides power, try switching it on. If it beeps, add the components one after another (CPU, RAM, rest), until it doesn't anymore (the last is your culprit). If it didn't beep without any components, its the board.

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I tried the PSU reset--didn't work. I don't have another PSU lying around though...Thanks –  Troy Oct 25 '10 at 21:02
    
without borrowing or buying one you're stuck, there's no way to reliably diagnose any further –  knitti Oct 25 '10 at 21:21
    
I read about this PSU jumpstart: overclock.net/faqs/96712-how-jump-start-power-supply-psu.html -- will that allow me to test if the PSU is working? –  Troy Oct 26 '10 at 22:53
    
If you short the right two contacts, you can tell the PSU its 'on'. Whether its working, you can't tell, because there's not any load on it. PSUs fail often "softly" by not delivering the right voltages and currents once some load is on them. –  knitti Oct 27 '10 at 0:06
    
Ok I tried with another PSU, now the computer comes on, stays on, but no beeps. I have tried connecting the front panel speaker on the pins both ways, but no beeps. What do you think? Also, I can't test video with this power supply unfortunately b/c it has no power for PCI-express. Thanks for your tips! –  Troy Oct 27 '10 at 0:27

Disassemble everything, give it a good blow (there's probably plenty of dust), and assemble again.

I had similar problem with dust in graphics card slot.

Also make sure that all cards and memory are pushed all the way down in their slots. A slightly 'raised' card can give similar symptoms.

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First off, are there any post beeps? If you don't have your internal speaker attached, do so and listen for post beeps, that will be your best indicator of what is wrong (you can find what each beep code indicates in your motherboard's documentation). When you try powering on with just the basics, make sure it is only one dimm of ram. Keep swapping out the dimms and try each one in a different slot. If you still have no success, you need to remove variables. Try with a different graphics card, different ram and a different power supply. If you still have no success, it is your motherboard (which based on the symptoms you describe, I'm leaning toward motherboard or power supply).

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No beeps; And I did try each DIMM one by one in each slot. Problem is, I have no other PCI-e graphics cards lying around, nor power supplies or compatible RAM. Thanks for ideas –  Troy Oct 24 '10 at 17:54

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