First timer

I don't know too much about this stuff, but want to know and learn more.

I have a Dell Dimesions 2350 that needs a mother board because the audio device has yellow question mark, and even if I try to reinstall it, it doesn't work. My question is what kind of mother board can I put in it? I believe it's a DDR.

Welcome, first timer. Be sure to take the time to read through all the guides, as that will make your visits more productive.

The 2350 is a good, reliable, but very old Dell Dimension... about 7 years old...
Best, cheapest, easiest thing to do is go to your Device manager and disable the sound list found there... then buy a decent sound card such as a Creative or RealTek...
You will then be back to normal.

Replace it with another Dell board... 2350, 2400, on up to 3000... but your connectors will be different above the 2400... and if you have never done it, you are in for some suprises.