Computer will not boot

[Guest]

i have a computer that is a couple of months old
Athlon X2 4200
Asus M2N-E - AM2 nForce 570
2GB XM2-6400 RAM
Sapphire Radeon X1900XT 512MB [pci-e]
Soundblaster X-Fi
550W power supply (thermaltake)

all of a sudden on monday after bieng turned off for 2 days (power cord
still in and powered) the thing won't boot anymore. All i get is a blank
screen..all fans and LEDs start up (including the fan attatched to the
x1900).
the 1900XT usually starts with the fan on full power, then dips to a quiet
setting..since this problem though, the fan sticks on 100% (i.e. really
loud). if i unplug the VGA card and try and boot, the mobo complains with the
usual beeps..same deal if i unplug the memory..i removed the hard disk (SATA
connection) to rule that out but it makes no diff with that removed.

ive tested the 6 pin molex into the VGA card and it reads a fraction over
12V on all 3 pins (3 at +12, 3 grounds). ive tried removing the 4 pin power
connector to the mobo and without that, the system powers down after a few
seconds so i think that the power supply is ok

problem is that i dont have any old vga cards to test in place of the
1900XT. considering the above, do you think the most likely culprit is the
VGA card? the three components i think it could be in order of suspicion are:
1. vga card
2. mobo (thou it does detect when the card is not present and complain)
3. power pack..thou again this worked for months up to the w/e.

 

[Dave B.]

I would try a new power supply first, you state "3. power pack..thou again
this worked for months up to the w/e", but so did all your other components.
The PSU is the most likely culprit, motherboard could also be the cause. How
long an item has been working is not a factor for determining failure.