computer problems. Can anyone help???

[Louwai]

Opened the box to have a look. As all VERY experienced PC techs would do. I haven't opened one of these for about 10yrs. Everything looks different.
First thing I noticed was what looked like the main power supply cables not plugged into either of the HD's.
Straight away I thought "no worries" but then the brain took over & I figured it must have been like that cause there's no way these plugs could just fall out. Then I noticed the 2 OTHER sets of cables going to each HD. Nothing like the old power plugs I'm used to.

Stuck a screw in the loose HD. Cleaned the dust out of the fans.

Plugged the power in & switched it on while looking inside.
(looking inside & cleaning dust out has always worked in the past)

A little green light on the m/board came on & the power pack was making sausage-sizzle noises. Still no fan movenment. Switched it off. Decided to switch on again just in case it changed it's mind.
This time a pop & flash from the power pack. Then everything dead. Not even the little green light.

So using my great PC knowledge, I reckon the first thing I need is a new power pack.

The existing (dead) one is a 400w. Should I put in a bigger one????

Then I guess I'll still have the original issue.

HELP!!!!!!!!