Hi Jerry Welcome to Answerpool
From what I can see you have done You have done the same things as I'd Do
Try this Remove all the Cards, graphics and sound card(If fitted) And then Start the Computer up and Let it warm up for 5 minutes(won't do anything) switch the Power off but leave the Powercord attached (dispels Static)
Locate the RAM Cards and Touch them Are they warm or Cold? Warm means they are working Cold Means Not working...(and all sorts of trouble)
But Sometimes a "none working" Memory stick can be due to the contacts not Being secure Note the 2 white security Clips Position Are they snugly pushed into the recesses(Indentations on the Memory Card? If the answer is No then there is a small chance that the Connection is NON Op Have to remove the cars by releasing both Clips together and the Card will Pop out of the Slot.
DO not Touch the Contacts otherwise the card is Scrap!
Fitting the card is done By inserting the Card
Loosely in the Slot There is a Notch in the Card to ensure the card faces the right way
Note open the clips out
Next Push the Card gently into the slot using your 2 thumbs on the Top outer edges apply equal(STEADY!) pressure and You will note that the 2 security clips will begin close as you push the card in till at just over 2/3rds the way It seems to Jam

...Next press the Clips together themselves and they will click into the slots I Mentioned earlier (job done)
Worth swapping ram boards around(Id you have One with the same Number)(id on ythe Lable ...To Order New Memory Write Down exactly
what it says on that Label there are 100's of variations...Mine is called
512MB PC3200 400Mhz Sometimes says
512MB PC3200 400mhz SDRAM There is another thing something called EEC this is an error correction circuit Tell them You don't want this, otherwise the price increases.
Pricing of a Memory stick depends on the Brand Name Kingston and Corsair are the Big names, but all makers have prices within a dollar or 2 of each other
If after swapping replacing the Chip over there is No change then I'm Baffled
Question is the Copy of XP Pro an original Disk? or a Copy? If its copied then then it useless as the Original disk has copy protection on it can get some odd Cab files to swap over but as a Whole it is useless
And I wander if the Original but used copy will work as its Keyed to 1 computer
An unused SP1 Original? Rare as hens Teeth.

Invest in a proper OEM SP2 copy @ $175?(Prices do vary) and its about 2 hours install time
Should go smoothly ...XP SP 2 is being withdrawn soon Be sharp otherwise You are going to Be forced to use Vista Premium (for the same price)
MS's next OS(after Vista) is Not due Out till late next year or early 2010