Cosmos Seedlings Dying

Hi,

My cosmos seedlings are have all suddenly started to curl up and die after getting discolour shrivelled leaves.

Can anyone help? First time growing them from seed and very sad to see them all on the way out. They were very strong and bushy last week. Planted in Miracle grow soil don't know if this could be a problem?

Don't want to plant them on if it's a bacterial problem.

Will see if I can get some pictures.

Any help much appreciated!

Thanks!

Miranda