If there are no fish in the tank you don't have to treat the water with ich medicine. You just have to keep the temp up and wait for a couple of weeks. Also turn the filter back on, otherwise stuff can just sit there(unless you're willing to wait a couple of weeks for the life cycle of the ich to die without hosts). Also, seachem prime does not cycle a tank. It removes chlorine, chloramine, heavy metals and such. It also helps promote a good slime coat that the fish need. Is your tap water from a well or a municipal water supply? If it's city water you most definitely will have chlorine which absolutely needs to be dealt with(with the prime) during each and every water change. Fish can't live for long in chlorinated water.
For cycling your tank...
http
/www.fishforums.net/index.php?/forum/291-cycle-your-tank/ please check out this link and read the topics. At the very least learn about why we cycle without fish before you make a desicion. And just running the tank won't cycle it either.