If your transmission was ok when you parked it, I would not worry about it. should be fine.

 

it doesn't matter if you just parked it before, and suddenly it is not working.
His probs are EXACTLY, what I have just encountered. the above dude is right; if you can shift when it is off, but as soon as you turn the key on, you cannot shift, you have a problem with your clutch kit; one or more of the parts-pressureplate, rotor, throw out bearing. Also secondary possibilities are the clutch cyl, slave clutch cyl, bracket plate is cracked on the floorboard, or the slave clutch forkpiece.
next prob is the tranny itself, synchros or other parts, which is just do a tranny rebuild and get it over with.
Thirdly, it could be both, you are in need of a new clutch kit assy., and a tranny rebuild!!!! This is what i needed, total cost was about 1500 bucks, parts and labor. Not including towing, or fluid drains/refills, or putting on the slave cyl,
that I tried to put on myself.