Motherboard or Power Supply Problem?

[Dwead100]

So I have a old MSI KT6 Delta
Version 2.1
G52-M6590XP
MS-6590 (v2.X)ATXMainboard (back from 2004).

It has a 500W Rosewill RV500S-2 Power Supply.

So my initial problem I thought it was my monitor cause I couldn't see a boot screen nor even a bios screen on boot.

So then I tried a different monitor (that I knew worked), same problem no boot screen for xp or even bios again.

So then I switched out the new AGP 8x 512 DDR MB video card with a ATI 64MB PCI VGA/TVO/DVI-I video card from a computer I knew that worked; I also didn't have the AGP card with the PCI in at the same time in either situation (and I knew the PCI video card worked). Still no bios or operating display on the monitor.

I then tried the WD 120 GB ATAT133 hard drive (with the XP Operating system; I put the hard drive under slave mode in the the different computer) in a different computer; the new computer recognized the hard drive--> so no hard drive failure.

I then switched and tried every ram module separately into a motherboard that I knew worked (it booted correctly with the correct amount of ram stated in bios and under the operating system).

I next checked the Dvd-ROM and CD-RW drives from KT Delta motherboard and left them in the powersupply. The Cd-rw would not open with the 500watt rosewell powersupply but when I switched it to a totally different motherboard and power supply. The CD-RW drive opened right away.

So my question is:

1. Is it a faulty power supply with bad connections (Or do I need to get a bigger one)?
2. Is it the CPU or motherboard-because neither video cards worked?

[Dwead100]

I also cleared the CMOS memory (when the computer was off; changed it to position 2 & 3; let it reset for 30 seconds; then switched it back to position 1 & 2) on the motherboard. Rebooted the computer and still the same problem.