Weird Dell behavior with memory upgrade

Okay, not specific to Flight Sim, but I do play it on my girlfriend's computer. She had me upgrade her RAM from 256MB to 768 MB, since she was having to swap a lot and was just slow overall. It's a Dell Dimension 4500. So I stick the RAM in, but it doesn't turn on until a good 30 seconds or so after I hit the power button! I was afraid I had fried the motherboard. RAM seems to work fine, and Windows recognizes it okay. Computer runs much better since. Anybody else seen this? I can only assume it was doing some sort of test of the new RAM before it actually showed signs of turning on.

Try to change the slots.
Put it in the slot that has the 256 the,and the 256 in the second slot.Are both in 333 or 400Mhz or maybe they have different clocKs between them?

Lets us know.

They are both DDR 333 RAMs. I hadn't considered swapping, and it only did this weird delay once after changing the memory. Now it works normally. Just kind of scary when you put in an upgrade, hit the switch and absolutely nothing happens for 30 seconds. No video, the hard drive doesn't spin up, the cooling fans stay off, and thought for sure I had damaged something. I pulled out the RAM and it did the same thing. It was while I was scratching my head on what could have happened then it suddenly turned itself on. Then I put the stick back in, and it delayed again, but only once. Maybe it's a Dell quirk.

When you power up a PC,the mobo will run a memory test
You can normally dissable it via the Bios