Some of the "lower priced" serial / usb comms cables will not work with the MSD s/ware, they use a cheaper / different converter chip in the cable. Also, you may need to download a driver for your USB port or just configure it depending on your version of windows. I had to download a USB/serial port adapter driver for the grid when I first got it years ago. However a newer, more recently purchased lap top (windows 10) did not require it and it really was plug and play. HTH's 
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
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