Hi, I've recently started using illustrator in my job and am currently experiencing problems with editing the text into a previously saved file. For some reason the file won't allow me to select any of the layers, I've tried sending the 'top layer back' only it seems asthough the whole structure is one layer?.... if that makes any sense.......... The file was originally saved as a JPEG so I don't know if this is what is not allowing me to make any changes??
If the original file was saved as JPEG it means that you can't edit it in Illustrator. Presumably the image is only on one layer – look at the layers palette if you're not sure. Click on the little grey arrow to the left of the layer icon to see if there are any sub-layers. I don't expect you'll find any. Try turning off the preview (Cmd-Y) and I expect you will see that there aren't any vectors to edit, only a box. Illie is a vector application and you will need Photoshop to edit a pixel file.
As Steve said - JPEGs are pixel images. Nothing you can or would edit in Illustrator. To retain editability, your only options are the native AI format and PDFs with retained Illustrator editing capabilities, from which you can of course generate a JPEG or any other format at anay point, but you would always keep the original vector files around, still.