Take the 2-minute tour ×
Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

I have a strange problem with my desktop PC. I tried different things to fix it with mixed success.

When I turn it on, it displays the BIOS/motherboard logo and then restarts. I can’t access the BIOS to edit settings because it restarts too fast. (I tried to reset the BIOS without success.)

I noticed that a capacitor from the graphics card was broken (it looked exploded) so I ordered a new graphics card and plugged it in. That didn’t help and it still reboots.

I tried removing everything that’s not necessary. I put a single one 1GB stick of RAM in the motherboard (usually it has four) and the computer actually started successfully (i.e., booting Windows). I then put in another stick of RAM and the computer still worked.

When I put in the 3rd stick of RAM, it didn’t boot anymore (again restarting all the time). I removed this 3rd stick and this is where it gets weird. I expected the computer to boot again because it is exactly the same configuration as before—which worked—but it didn’t work anymore! Now it is restarting even though it used to work.

The next test was to put a single of stick of RAM in the motherboard. It worked again and Windows would boot. I tried each stick of RAM in each of the slots, and it worked every time, so all of the RAM and all of the slots appear to be okay. It only seems to stop working if there are three or more sticks installed at the same time.

Further, the CPU fan is quiet when the system works and is loud when it does not.

Anyone an idea what might be wrong?

share|improve this question
    
Try going back to just 1GB and see if it still works. If so, move that stick of RAM to a different slot and retry. Do this for each of the RAM slots to determine if it is the slot that has the problem. It is possible that the 3rd stick damaged something, but fortunately, is usually unlikely. –  Synetech Jun 24 '12 at 16:24
    
I putted the 1GB RAM in each slot and it worked in every slot (it booted until windows). I also putted every stick of RAM in the first slot and it booted with every stick op RAM. I'm going to try now to add more sticks of RAM, so far I think it was always when I put in the 3rd that it started to fail. –  Joris Jun 24 '12 at 16:39
    
I also noticed that when the boot-up doesn't work, the fan (which drives the air from the CPU outside) starts to work extremely hard. When the boot works, that fan almost doesn't make a sound. –  Joris Jun 24 '12 at 16:41
    
Hmmm, interesting. So all of the sticks of RAM seem to be good, as do all of the slots. That bit about the fan might be the clue. When you said that you tried resetting the BIOS, what do you mean? Do you mean by entering the BIOS? Does you motherboard have a special key that you can press/hold to reset the BIOS without entering the BIOS at all? Does it have a jumper or something on the board that you can short-circuit to clear the BIOS? What make/model is your motherboard? –  Synetech Jun 24 '12 at 16:48
    
I (1) removed the motherboard battery and (2) switched the reset jumper. (clear CMOS) It's a P35T-FB (Fujitsu) uk.ts.fujitsu.com/rl/servicesupport/techsupport/Boards/… When I was able to enter the BIOS I also reset it to default settings. When I added sticks of RAM I was able to reproduce the problem again, stick 1-2 works, when I add a third stick it stops working. I'm going to read now some more in the motherboard manual to see if I find anything there to try. –  Joris Jun 24 '12 at 17:03
show 2 more comments

2 Answers

Well, let's take a guess. If you took out all of the RAM, added it in 1 chip at a time, and then it stopped working on the 3rd chip, I would say that chip is bad. Throw it away (make sure it is the right one.) and continue on.

share|improve this answer
1  
Yeah that's what I thought, but then when I removed the 3rd chip - and only the first two chips didn't work anymore. (in exactly the same configuration that worked before) I don't think this is suppose to happen if it's just the 3rd chip that's defect? Then everything should work without the 3rd chip? –  Joris Jun 24 '12 at 16:19
    
Try @synetech's suggestion. –  ekaj Jun 24 '12 at 16:20
add comment

You said that the CPU fan is loud when the system doesn't work, and that the system started to restart again after putting in and then removing the third chip.

Perhaps the CPU is overheating? If it reboots even after removing the third RAM stick, turn it off and let it sit for a while, like half an hour. Then see if it would run.

Take note of CPU temperature in BIOS. When I start my computer and go to BIOS it usually sits around 30-something degrees. Over 50 without any workload is bad, I think.

If the computer runs after a while of inactivity, and if you see the temperature rapidly rising in BIOS, perhaps you should reapply the heatsink. Unscrew it from the motherboard, pull it out from the CPU, wash both heatsink and the outside of the CPU with rubbing alcohol, dry it out, and then reapply new thermal paste and fix the heatsink into the CPU and motherboard.

share|improve this answer
1  
> Perhaps the CPU is overheating? Yes, I considered that already, but it seems strange that it would only heat up if more than 2GB are installed. What would account for that? –  Synetech Jun 24 '12 at 17:46
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.