I loaded Sketch up on a new computer and my old projects are not available when o sign in.
Your profile says you are using SketchUp Pro. That version of SketchUp normally saves to the local, internal drive. Figure out where your files were saved on the old computer and copy them to the new computer. You could upload them to your Trimble Connect storage from the old computer and then open them on the new computer via File>Trimble Connect>Open.