Refer to Sashamorning's Walkthrough Page Here: Mr. Pumpkin Adventure Walkthrough
Except, as of 1/3/18, it is incomplete. Perhaps you came right from that walkthrough page.
It's missing two things:
1. When you get to the warehouse, you must finish the puzzle on the left side of the computer by clicking the box that the cursor is hovering over. This makes the left garage door open and reveal the blue cube.
2. Towards the end of the chapter, the Walkthrough page omits the solution to the puzzle with the red, green, blue and orange cubes. You can view a photo of the solution at: http://gamersunite.s3.amazonaws.com/uploads/comments/432311/...
(Credit to Aileen Hung)
Again, you must finish the last move of the puzzle after the screenshot - this time, by moving the green to the final open space at the bottom-right corner.