Currently, power supply 'system', motherboard, and so many other
parts are all 'unknown'. Your task is to move each system or
component from 'unknown' to either 'definitively good' or
'definitively bad'. That means numbers. That is not possible by
shotgunning.
Is it a power supply? Another recommended shotgunning. To replace
power supply. Well, it's called a power supply 'system' - more than
just a power supply. Replace a power supply and system still does not
work? What was accomplished? Everything is still 'unknown'.
Power supply 'system' can make everything else appear defective -
especially when supply is a cheap one that many computer techs (who
don't know how electricity works) recommend.
Do a two minute procedure using a tool "so complex" as to be sold
even to K-mart shoppers (and Wal-mart, Lowes, Radio Shack, Tru-Value
Hardware, Sears, and other 'guy' stores). Numbers from a 3.5 digit
multimeter obtained using "When your computer dies without
warning....." starting 6 Feb 2007 in the newsgroup alt.windows-xp
at:
http://tinyurl.com/yvf9vh
Numbers either put the entire 'system' (not just a power supply) into
'definitively good' or 'definitively bad'. AND numbers make possible
another, who has far more knowledge, to provide a useful reply.
Notice this poster does not post wild speculation.
If power supply 'system' is 'definitively good', then 1) there was
no reason to waste time and money buying and installing another
supply, 2) we move on to other suspect, 3) have not made the
problem exponentially more complex by shotgunning, and 4) would now
have more useful ideas from one who even designed computers 30+ years
ago.