I've constructed PC, which worked well except the fact that it was necessary sometimes up to 10 times to press the power button to start. After that there was no problem to work days along. Since it's Athlon, which tends to overheat I decided to change the CPU fan with newer one, and after that came the problem - it doesn't start at all - 2-3 seconds and shuts down, not booting at all. I checked the power supply by making short between 14 and 16 pin, and it worked normally. Removing all hard drives didn't affect the situation. Only when I remove the both RAM it doesn't stop, only with the fans working and making short beeps every 2-3 seconds. Putting them back, it was again shuting down. The same was by changing the positions of the RAMs or exluding one or the other of them.
I'll be gratefull if somebody could tell me the reason.

Hi,

This sort of problem is usually caused by the PSU. Have you used a multimeter to check the voltages on the 3.3/5 and 12V rails? That would be worth doing.

Also, depending on the components in the system, your PSU may be struggling with the devices it's using. You have tried unplugging the HD's which is a good start, try booting with just the MB/Memory and CPU (remove all PCI cards) and see what result you get.

It could be that one of your Memory sticks is the problem, I couldn't understand what you meant in your last post about the memory.

Good Luck

Shaun

The romoval of the pci cards didn't change anything, and for the power sypply that's my problem - I don't have now multimeter. Soon I'm going to try my RAM on another working pc. I wonder if it could be CPU problem ?

It could be that your mobo is shutting you down because it feels that your new fan is not high enough rpms or else is not drawing enough current in the case that your old fan did not have rpm monitoring. This was a foolish implementation of thermal protection offered by some mobos in the past and you have no ability to change it - you are being shut down because the mobo thinks you are about to overheat because your fan isn't screaming along like the stock fan.

If you have an 80mm fan on your new cooler, it will produce these symptoms.

You can:

1 - go back to the old cooler

2 - go buy a 50ohm, 5W resistor and solder it across your new fan's two wires, causing the cpufan mobo port to give out higher total current, essentially faking out your mobo (a solution I used a year ago, see my post called "my motherboard is a retard")

3 - plug your old stock 60mm fan into the cpufan plug and your new fan into some other plug, so the mobo thinks the stock fan is being used. Put the 60mm fan somewhere else in the case. If you don't like its loudness you can trim off a portion of its blades to quiet it some.

4 - Do number 3 above and go into bios and turn off cpufan rpm monitoring. Then restart and throw away the 60mm fan. I would not count on the bios having this option though.

The quick way to test if this is the problem is to plug the old 60mm fan into the cpufan plug and start it up with the memory in.

The reason the system does not shut down when the memory is taken out is because the bios program never loads so your system's autoshutdown doesn't kick in.

Or it could be something else altogether...

Well, I plugged working power supply and again no result. I checked the RAM by another pc and it appeared to be ok. Then what else could be - the CPU, motherboard ?

Have you tried Johnoh's suggestion?
Do you have a 60mm stock fan you can use?

It could be the mobo cpu, but I would start by truly eliminating the cpu fan issue that Johnoh identified.

When you say you 'plugged working power supply' what do you mean? Is the PSU more powerful than the old one?

Did you test the rails on the PSU?

Shaun

By working PSU I mean PSU which currently is working in another PC, and it's more powerfull then my. I put back the old fan, by which the PC was working before and PC doesn't work even with it.