Strange boot probs

[Mjolnir]

Working on a friends compaq PC - 900 Meg CPU, 512 RAM, DVD/CD RW 40 Gig HDD - has intermitent boot failure/lock up/freeze

Symptoms:

power on - fans run, CD/floppy leds light, keyboard lights flash, HD led lights, monitor led stays amber, no compaq spash or video on screen, HD led goes off after 10 - 12 secs - then nothing - (seemed like no BIOS)

Turn the PC off and back on - sometimes it would boot to the windows desktop and sometimes it would repeat above - even if it booted sometimes it would just stop - could not open task manager - nothing - had to turn off and then turn back on - had my friend pay close attention to when and what he was doing, even time of day but found nothing to link the failure anything

Action taken:

1st thought cmos battery PC about 3 - 4 years old - changed, reset cmos - same
2nd checked all cables, edge connectors, power - all clean and tight - same
3rd replaced HD ribbon cable - pc booted and ran all day yesterday - ran anti-virus, adware, disk cleanup and defrag left pc on overnight this morning frozen - on restart no boot
today - disconnected CD/DVD - no boot - removed RAM one by one - no boot - tried to boot from utilities boot CD - seemed to get half way through loading from CD then stopped - tried twice - same

I believe two possible culprits: BIOS chip - non removeable or motherboard

Any suggestions would be greatly appreciated before I tell him his PC is now a door stop !

Thanks folks

[Catweazle]

Romove all addin cards. Disconnect all drives, both power and data cables.

Power up and press the <Esc> key repeatedly as soon as you hear fans etc start to operate. The BIOS POST information is usually hidden in Compaq systems and pressing <Esc> during power up makes it visible.

Your system should display POST info until it reaches an error, and give you a hint to the source of problems. Removing all cards and components will allow POST to run to the point of detecting drives at least.

Add back the components one by one to ensure that they are recognised correctly in the BIOS POST info screens. Add your hard drive last, so that you are not constantly trying to boot into Windows and have Windows also detecting components.

There will be one or more internal components which are stopping the system from booting. An incorrectly attached power connector, a malfunctioning component....

With 512Mb of RAM installed in a 900MHz PC, it could even be a mismatched RAM module which is causing the problem. Ensure that initially you remove all but one RAM module.

[Mjolnir]

Tanx

Cat will try all this today