I have a problem with my F80.. When i flip the switch to M for my 28-80G lens and my Tamron 24-135mm, i cant seem to do manual focussing.. the focussing ring remains tight but autofocus doesnt work when i half press the shutter release... Anyone has the same problem or can shed some light ? IS it my lens or the body?
As it affects both lenses I would initially suspect the body. For a quick check, firstly can you move the focussing ring when the lenses are off the camera?
Secondly, take the lens off the body, locate the AF coupling, this looks a little like a screwdriver blade and is located at about 6:30 or 7 oclock on the lens mount. With the body in S or C, this should be proud of the mount by about 3 or 4mm (ish), with the body switched to M this should retract completely into the mount.
From your description of the fault, it sounds like this isn't fully retracting, as the M position also turns off the AF function it would seem that the AF mechanism is still connected, making the focussing ring difficult to turn.
It sounds as if the body is faulty, if under warantee then take it back to where it was purchased. Failing that you could try a little pressure to see if that would move it back or ideally take it in for repair. My guess would be that a spring has failed and so will need a proper repair but I guess it could be a little sticktion. All things considered your probably much better off taking it in for repair, much safer that way.