Car sitting in my garage for last few weeks not driven. I went to drive yesterday and pushed in clutch but it didn't pop back up. I have not had any problem at all so this was a real surprise.

Either a return spring has broken or come loose, or a seal on the slave or master cylinder on the clutch has failed. Check for fluids leaking inside or under car which would point to the hydraulics. A visual inspection of these areas would also reveal a loose or broken spring.

clutch slave cylinder mounted on bell housing underneath car.