PC Runs slower after installing more RAM?

Hello everyone,
Today I dropped by my Grandfather’s house, who happened to be getting rid of his old (assembled around 2003) Dell PC. It had two 512MB sticks of RAM in it, which he let me take home.

So I Crack open my case, and plug them into my second and forth RAM slots (first and third contained my two current 512 sticks of Kingston value RAM.)

I tried to boot up, and I wouldn’t get a screen signal. Shut the PC off, switched the RAM position around (so that the new sticks were in slots 1 and 3, and my Kingston was in slots 2 and 4). And it boots, although I’ve noticed a real performance drop. What gives?

The ram from the DELL is just standard no-name DELL RAM, and the PC is completely stable, it just seems to perform less.. I thought it would perform better with more RAM?

Thanks for your time!