2003 Chevy Silverado Key won't turn, steering wheel unlocke

We bought the truck from a wrecking yard and seem to have been given the right key as it is the same one that GM cut for us, it opens all doors, but won't turn the ignition. We have tried WD-40, jiggling the lock and pushing up on the shift lever, it won't budge! I did notice that the driveshaft has two indentations on it and was told by the previous owner that the tow truck driver undid the brake cable to allow the truck to move. Have any ideas?
Thank you for your time! Nancy