ken, if you can find the mtd model number on the mower and post it here, we can try to find a manual and get specific about what is happening. Generically, it sounds as if either your transmission shift linkage is jammed/bent/broken/out of adjustment, or the selectors are jammed or worn inside the box. It needs to be fixed, or you will end up using clutch-slip to do the job of the gearbox. It seems to be a decent mower, its best to get it working properly so you can rely on it in future.
