Nissan Maxima clutch problems

5 times over the past 18 months, I’ve tried to start my 2004 Nissan Maxima 6 speed manual transmission car (48451 miles) and found the clutch peddle depressed. I’ve checked the fluid and it was full. Repeated prodding did not work. It wil come up again only after it sits for at least 5 hours. I’ve taken it to the sdealer twice and they say they can’t find anything wrong. The last two times this happened, I had to get it towed back to my city. What should I do? I don’t want to have to buy a new car.