1) Your Not.hdl must be in the same directory as the Not.tst file you are loading.
2) Make sure that you don't have a Nand.hdl file in your directory. Some people flail around a bit getting started and leave an empty Nand.hdl laying around.
If you can't get it working, email me your Not.hdl, .tst, .cmp, and .out files to
This is extremely unlikely to be a Hardware Simulator problem; it hasn't changed since Nov 2006.
Make sure that you are working directly in the Nand2Tetris/projects/01 directory (folder). This directory should contain all the skeleton .hdl files and all the .tst and .cmp files. If you made a myChips subdirectory, or the like, it will not work because the test files load the .hdl file from their own directory.
It is very important that you implement the chips in the odrer listed in the book. If you try to build Or before you build and test Not, it will not work because the And chip requires the Not chip to be working. For this reason I would expect that you would see all of the chips not working when you copied code from the book.
Be certain that you don't have a Nand.hdl of any sort in your directory. Nand is a built in primitive and any attempt to make one yourself will cause Not to fail.