I tried to turn on my computer last night, and I CANT get to a POST.  My wife had been on the computer about 2 hours earlier and said EVERYTHING was fine at that time.  So, here is the full story:

I turn on the computer, and there is initial activity.  This is stuff like the processor fan, power supply fan, and case fan all start, the CD drives start to spin and their activity lights come on.  Then.... nothing.  

Here is my current system config:

Motherboard: MSI K8T800 NEO2-F
Processory: AMD 64 3500+ Slot 939
Memory: Kingston DDR333 PC2700 512MB (x4)
Hard Drive: Western Digital 200GB 7200 SATA
DVD Drive: PIONER DVR-108 DVD+/-RW Dual Layer
CD Drive: Samsung 52x/32x/52x CD-RW
Video Card: Radeon RW9600-256MB
Sound Card: Voyetra/Turtle Bay Santa Cruz
Power Supply: ATOP 500W Power Supply
Operating System: Windows XP Home

I need to get this up and running ASAP - if anyone can tell me where to look that would be much appreciated

The first thing to do is to open the case and make sure that no cables attached to any drives have worked loose. This includes power cables with molex connectors.
If that doesn't help, post again and we'll go from there.I have had that problem several times before with a western digital drive, actually three, so I switched to a different brand and havent had that problem since. Before you go out and buy another hard drive, if you have an old drive, TRY it, if not borrow one. Also check to see if your cpu is BURNED up..Oh does the monitor come on? Is it black? Could be the video card if it is. Anyway check all the possibilities...