there are lot of dead leaves, and its starting to turn a little yellowish.

What is your general location/growing zone?Are they outdoors? What kind of exposure? Do you water them? Is there a drainage hole in the container? How deep is the container and what kind of soil are they planted in?...These are very hardy Sempervivums, easy to grow so pls. answer questions to find out what the problem is.

What happened to these plants? They looked fine to me.

It's a sempervivum of some sort, but it looks alright to me, and it's normal for the lower leaves to die

Thanks for the comments, i thought it looked like it was dying. I’m a newbie at this! But it’s doing great!

That's great to hear Lenore! Best of luck with them.