Computer will not start. Thought I tried everything, I'm baffled. Open to suggestions here.
Installed new mobo, ATI All in wonder PCI expressx1900 card, new Antec 500w PCI approved power supply; tested good by ATX 12V Version 2.0 power supply tester, new Antec mid tower case, new AMD Athlon 64 X2 3800+ socket 939; proper seating and heat grease has been verified for CPU and ASUS CPU cooling fan attached to top. The (ASUS A8N32 SLI-deluxe) green light comes on when power supply switch is turned on. But nothing works or turns on when case on/off button pushed. I have tried new power supply cord, plugging into another Ac outlet on different circuit. I have built several computers and this problem really stumps me! Someone please help.
{The above configuation worked,(powered on and I loaded OS), then turned off. Next day system would not come on}.

Hi have you checked that no wires have come of.

Hey Brain Damage
I have and figured out the power problem last night about 2am, however now there is no signal to my LCD monitor. It turned out the wires from the on off button on the case were 1 pin over, incorrect position. I have tried moving the IDE LED wires to make sure they are on correct; now the front panel case LED lights up. I checked the power to the HDD and it tested good and I can feel the HDD spinning upon power. However when I 1st turn on my LCD monitor; before I power up computer; the green LED comes on the monitor and then the ACER logo shows on the screen then a moving grey rectangle shows "NO SIGNAL", the green monitor LED changes to yellow.
What is wrong now?
PS thanks you replying & Pink Floyd rules!!!

before I power up computer; the green LED comes on the monitor and then the ACER logo shows on the screen then a moving grey rectangle shows "NO SIGNAL", the green monitor LED changes to yellow.
What is wrong now?

you wont get any signal to the monitor until the PC sends some

have you tried the monitor on another machine or another monitor?

are you getting any beeps from the machine?

Just tried another monitor I know worked; Iiyama Vision Master 17". Same message on monitor=no siganal. No beeps from machine.

I would check the video card is seated properly

Video card is seated. No signal still.

Thanks for all your help. No more help needed.
Take care.

Thank you for the thanks

Glad you're all sorted