It looks to be root rot. It shouldn't have mattered if part of the stem was buried or not. But the soil surrounding the root mass looks really wet. You still can save the plant by cutting off all the rotted parts at the bottom of the stems and rooting the healthy stems. You need to let the cuts heal for a few days so that they wont rot again. Jade is a succulent, so it doesn't need water constantly, the soil needs to dry out between waterings or the roots will rot. When the cut has healed/dried out put them in soil BUT don't water the soil at all, keep it dry but you can mist it. once your stems show signs of rooting then you can water it. but not too much and let the soil go dry still. Also, don't let them be in full sun, they will burn.

I take back what I said about the stems being buried. It may have played a part in rotting easier.

well part of the wetness is from me using yhe hose to remove some of the dirt..the pot was really dry.

I was talking to someone and he told me a good rule of thumb was that drying starts at the edges of things and rot starts at the inside and works out. This is good to know when looking at leaves and such. It might be the same here. I vote for Rot.. What is your soil like? is it peaty or gritty? I better shut up because I don't actually have experience with Jades.

i vote for rot too. in addition to outside in vs inside out, this seems to have happened bottom up. dehydration i would expect to see some dropping/shriveling of leaves before a massive keel over like this.

I vote for rot too...

Mike

i thought it was rot as well... the leaves arent shrivled up, just some have brown spots as if they were sunburnt.. i didnt any bugs of any sort (now im second guessing, hope not i do t want the bugs to get to my 30yr old jade :( crossing fingers)