Simple RAM question

I am running a P5K SE/EPU by ASUS as a mainboard. I currently have 2 gigs of DDR2 ram in there atm by "Super Talent" And everything works fine, however I want to add 2 512 sticks of DDR2 kingston ram (Kingston KHX4300D2K2/1G 512MB 533 ) Why does my computer lock up when I start it up when I add the kingston RAM? Do I have to set it up though BIOS since they are different?

Well ram is an extremely fussy beast, many times people never have a problem and wonder why those like myself go to such lengths to get the correct ram, for starters ram has to be compatible with the board, then it must be of the correct spec.
Now when you add extra ram at a later date it's essential from a performance point of view to get the same spec ram, mixing makes will work, BUT, it "may" throw a spanner in the works and\or cause a performance hit due to working with another make of ram, and if that didn't sound like enough trouble then throw in the fact sometimes boards will only accept a very specific kind of ram, in my time I've seen a system refuse ram unless it was a specific size stick (quite rare though), or a more common one is some will not work with single or double sided ram, so as you can see there are many factors.

Lets start with the existing ram, can you tell us the exact model\spec of what was working in the system ?
I have just looked on Kingston's site and they do not list that ram as being compatible, they list the following for that board:-

Memory upgrades:
KVR667D2N5/512 512MB 667MHz DDR2 Non-ECC CL5 DIMM
KVR667D2N5/1G 1GB 667MHz DDR2 Non-ECC CL5 DIMM
KVR667D2N5/2G 2GB 667MHz DDR2 Non-ECC CL5 DIMM
KVR667D2N5K2/1G 1GB 667MHz DDR2 Non-ECC CL5 DIMM (Kit of 2)
KVR667D2N5K2/2G 2GB 667MHz DDR2 Non-ECC CL5 DIMM (Kit of 2)
KVR667D2N5K2/4G 4GB 667MHz DDR2 Non-ECC CL5 DIMM (Kit of 2)
KVR800D2N6/512 512MB 800MHz DDR2 Non-ECC CL6 DIMM
KVR800D2N6/1G 1GB 800MHz DDR2 Non-ECC CL6 DIMM
KVR800D2N6/2G 2GB 800MHz DDR2 Non-ECC CL6 DIMM
KVR800D2N6K2/1G 1GB 800MHz DDR2 Non-ECC CL6 DIMM (Kit of 2)
KVR800D2N6K2/2G 2GB 800MHz DDR2 Non-ECC CL6 DIMM (Kit of 2)
KVR800D2N6K2/4G 4GB 800MHz DDR2 Non-ECC CL6 DIMM (Kit of 2)

And the QVL list from Asus themselves do not show what you have got as compatible, so this may well be why it's not working, when choosing ram you should always use the ram makers Configurator or the ones suggested by the board makers, this ensures you get something guaranteed to work.
Best advice given what I've found so far is to return it and get something listed here, might even be worth ditching the current ram as it's so cheap these days, it takes away the "will it play nice" worry, sorry it's not much, but hope it helps a bit.

Ah thank you your post, was very informative. Yes I do believe this Kingston RAM will not work. Although it is OK, seeing as how it is just left over RAM that my brother gave me after his new built yesterday. I Suppose there is always craigslist.