Psd to Jpg not working

I'm having a problem with Jpgs, ive just updated my system software and after re opening Photoshop and trying to save to jpg its doing something really odd....My artwork is flattened and is in 8 bits RGB which is normal, select jpeg format, go through the usual settings/size hit save and its still saving as a psd file even though ive saved it as a jpg. if i try to open the now saved psd file it won't open, but if i manually replace the .psd to .jpg it will open. so i dont understand why its not saving as a jpg now? any suggestions?