The timers use a serial cable. The computer will need to have a serial port to accept this cable.
It is always better to have a built-in serial port, but all-in-one PCs often do not have them. For these you can use a serial-to-USB adapter to convert the signal.
We strongly suggest using the Plugable USB to RS-232 DB9 Serial Adapter (PL-2303HX Rev D chipset) http://plugable.com/products/PL2303-DB9. They can be bought on Amazon with two-day shipping.
For Windows 8 and 10, the adapter must be a Rev D chipset. We have had very good success with the model above and other models may not work with newer operating systems.