Al wrote:

In trying to figure out why this atx pc won't start,
I carefully looked at the motherboard. Some of the
blue 'can' capacitors are straight across the top,
with the X shape. But others are bulged up.

It's a sign of impending doom, and if left unfixed may eventually cause
failure of the components connected to them, like the toroid coils and
MOSFETs. I had one MOSFET heat up enough to turn from black to light
tan, and after replacing the caps and installing a new MOSFET, it ran
at over 100C, even with a big copper heatsink, because the chip driving
it had been wrecked, too.

Probably the safest way to replace caps without using special equipment
is by cutting them off on top -- right through their cans, so that the
pins can be unsoldered individually. But I learned that multilayer
boards need a lot more soldering iron power than normal, and even 40W
may not melt the solder right away while 50W will. I used 2mm copper
desoldering braid to clean out the holes because I didn't have very
good luck with solder suckers.

I'd replace even the caps that still look normal because recently one
of my Antec PSUs had one cap bulge while the others were not only still
flat but also tested good with an ESR meter. Yet one of those "good"
caps bulged a week later and showed high ESR.