I have Intel D850MV motherboard with two 256 MB and two 128 MB RDRAMs, AGP video card with 128 MB on-board RAM, Samsung 40 GB HDD (ATA) and DVD R/RW drive. Upon plugging the computer to the power source it powers up before the power button is pressed. The power LED, HDD indicator LED and two LEDs on the motherboard light up. The cooling fans on the processor and inside SMPS start rotating. But there is no activity and no display on the monitor. There are no beeps. The power switch and the reset switch do not function. However if power switch is kept pressed the computer shuts down. The CPU and video card heat sink and hard disk become warm. The DVD LED lights up initially and drive door can be opened and closed. What could be the problem? I am located reasonably far from authorized service outlets. Any advice useful for my local service person will be most welcome.

Is this a problem that just started or is this a new build?

If it's a new build check the CPU for bent pins. Pull the motherboard and do bench check. The fact that it shuts down when the power switch is held in, indicates that the motherboard is working to some extent.

That's definitely not a new build guys. RDRAM and the Intel 850 chipset suggest that this PC was built sometime in 2001. When fans and lights power up, but nothing else does, 75% of the time the power supply is the culprit. First of all, reseat all of your RAM, PCI, and AGP cards. If none of that works, borrow a 300W+ power supply from another computer or a friend, plug everything in and see if you get anything. If that doesn't work, then I'd say that the power circuitry on the motherboard is toast. EDIT: Forgot to suggest that you should also test the system with all unnecessary cards and peripherals removed from the system. For example, remove the sound card, modem, NIC, hard/optical drives, and all but one pair of RIMMs (ram). Remove USB and other devices except the monitor. Test the system with only the CPU, a pair of RIMMs (ram), and the video card inserted. Super Pentium III: NOW WITH 7950GT AGP! PIII-S cpu overclocked to 1.66GHz--As fast as a 2.5GHz P4! 2GB of PC2700 memory QDI Advance 12T board Audigy 2 Vista Home Premium

jack I meant did the OP just assemble this rig or did this problem just crop up.

You should have a set of pins and black plastic jumpers on your mother board ,have you been changeing these around? Consult manufacturer for default/correct settings