Well I get the "cannot render file" message when I try to play a media file that has not completely finished downloading. So maybe you can try downloading the file again and then try playing it again to see if it works. Or maybe you don't have the right codec installed to play the file. What kind of file is it: AVI, wmv, mov, rm or what?
Well JPEG files are just pictures so you should be able to open them in MPC, but it's not the best app to use as most use it strictly for videos files. For picture files, like the jpeg you have, you should use a photo viewer like the default one that comes with windows. It should open the pic with a doulbe click, if it doesn't right click on the pic, select properties, under "Opens with" click the Change button. Select Microsoft Photo and Fax Viewer as the default app to open the file with, click ok, apply, and ok again. Now double click on the pic and it should open. If the viewer says "No Preview Available" the pic is corrupt and can't be opened.
