Power-up issues

[lost-and-found]

I'm working on an old PC. It's a K6-2 500Mhz, with a luckystar MVP3 motherboard, and an AT 250W PSU. When the PC is off for a while (at least 15 minutes) when I push the power button, everything spins up (including fans, hard drive, cd-rom, etc), but I get no "beep" and nothing shows up on the screen. If I push the reset button, or power it off and on, the PC will end up working fine. I cannot for the life of me find what the problem could be. I have tried unplugging all the expansion cards, with only RAM, the HD, CD-ROM, FD, and video card connected, but I still have the problem.

Edit: not the PSU, not the Video card, not the drives, not the peripherals, not RAM...I'm guessing the motherboard is just DUMB!!!!

[bailey]

it may be possible that the cmos battery is very weak and not allowing it to boot properly, check and or replace the battery and see how it boots then, you will need to go into the bios to reset any settingg that are not default.

[lost-and-found]

Tested with a good battery and still the same problem.

The PC has had several problems, which is why it was brought to me. First: the owner said that after it was on for a certain time suddenly the screen would just lock up and change into big color bars. Second, the RAM reported by the BIOS was incorrect, I've tried different ram modules, etc...I changed the hard drive IDE cable and it seems to have fixed the incorrect RAM issue. I have yet to experience the color bar problem.

Now the only problem is that power up issue.
So far tried: changed video card (even tried AGP instead of PCI), disconnected all drives from PSU, removed PCI components, removed the CMOS battery.

[lost-and-found]

update: I'm thinking it's the PSU. Upon contacting the owner a moment ago, I've discovered that he heard noises from the PSU (probably dying fan). I've not experience that yet, but I'm thinking that when one first powers the machine on, the PSU cna't handle the load and doesn't send enought power from teh start. However, when the reset button is pressed, or the PC is turned on right after turning it off, the PSU capacitors still hold enought charge to not cause a problem when powering up. I dont' have a reliable AT PSU so my testing will be limited .