There is a "sludge" in my fuel line, it was cleaned out and the car was drivable. Soon after I was having trouble starting my vehicle. I suspect that the starter is no longer working, but I also think that someone may have put something in my gas tank. I have read that sugar does not normally cause this much damage. Does anyone know what could and what I should do about it?

You did not mention if it is diesel or petrol. If it is diesel then the sludge will be a moss contamination the grows in the fuel when there is water present. It is black to motley grey and is a bit slimy. It occurs when the fuel tank is not filled completely after use and the hot fuel from the injectors cools down creating moisture (condensation) in the tank. IT can be cured with a liberal dose of diesel fuel conditioner but you will have to change the filters a couple of more times . IF it is petrol the amount of sugar used would be so much that nobody could afford to do it. so check for some other problem . Dirty fuel from a lower quality servo will be more likely the answer to the sludge and there are fuel conditioners that will help here.. There is no connection to fuel and starter problems so check the battery by having a load test done on it to check for failing cells. Starter motors either work but do not have enough power to turn the engine over (battery-dirty terminals) or do not work (starter motor --relays --wire connection fuses). Change the fuel filter weekly if necessary and moniter the amount of contaminant getting stopped by the filter. Flush out the tank in it doesn't get less. By a lockable fuel cap to prevent further problems.