Need solution : Is it the Motherboard or SMPS or both ?

Is it the Motherboard or SMPS or both ?

I've got an old PC lying around with the following configuration -

P4 2.4 Ghz Socket 478
RAM - Hynix 256mb DDR
Mercury KOB845GL NDMx v1.2 Onboard Intel 845GL Graphics Chipset/CMI9738 Audio
SMPS - 300 Watts LPT2
Samsung 40 GB HDD SP0411N 7200 RPM
Sony DVD Rom DDU 1622
Realtek 8139/810x Family Fast Ethernet NIC
Samsung PS/2 SDM 4500 P KBD
Logitech M-UV96 Optical USB Mouse
Samsung SyncMaster 753S 17"

OS - Windows XP Dark Edition V.3

SYMPTOMS -

1. - PC shuts down randomly and once it shuts down it will not boot up instantly.On restart I only see the Power LED glowing, HDD LED is off and there's no beep or display.But it does boot up normally if I start it after a couple of hours.

2. - On rare occasions,only the display goes off but I can see the HDD & power LED glowing.

3. - I cannot add two RAMs or attach a second ROM/Writer anymore.When I add an extra memory module it either gives irregular beep codes + corrupt display or no beep at all + no display.In case it boots up the system perfomance is really bad and system crashes sometimes.On adding a 2 devices on IDE 2, the slave refuses to even read a normal CD and the master reads very slow.Did not boot on two instances.Both RAMS used to work in both slots earlier and the pair of IDE 2 devices as well.

WHAT I HAVE TRIED -

1. - Decompiled and Cleaned the system.
2. - Switched OS
3. - Cleared CMOS and changed every possible BIOS setting
4. - Flashed the BIOS
5. - Stripped down the system to Mbd,Processor,RAM only during Symptom 1 and there was no beep/display on removing the memory module either.
9. - Ran diagnostics on the system from a boot CD and all devices passed.

The only thing that's left is to borrow an SMPS from a friend which is difficult or take the entire tower to his place and check but I've kept that as the last resort.Has anyone encountered this kind of a problem ? Is it the SMPS or the mainboard or both ?

Well, If you onle had a second PSU then you would have checked whether it is just a normal PSU problem or the motherboard. How old is this rig, if in warranty then try changing the motherboard.

Hi,
which OS you were using previously and to which OS you have switched to.

Have you properly formatted your Computer.

Regards,

@unidentified
The mobo and SMPS was bought way back in 2003.I did try to get in touch with Mercury but I think they have shut down.Their website was last updated in 2005.

@Howerski
Yup.I format the computer completely atleast twice a year.Windows Server 2003 and Windows 2000 Pro were used earlier with the original configuration.But that was for a year or two.After that it was Windows XP + different Service Packs/Modded versions.Funny thing is that I installed Windows Server 2003 again and it gives the same issue.

I forgot to mention another issue which just took place and I managed to get the system running after like 4 tries.The hard drive is not detected sometimes.Says - Boot failure.Attach hardware blah blah blah.