(You can check if it's iced by opening up the unit-- the coils will literally be covered with ice-- you might need a hex wrench and should turn off the power to it before doing that. Or, if it's been running long enough, the pipes to the outside might even have ice on them.) To fix it, put in a clean filter, then run just the blower for a couple of hours or so until all the ice has melted off.

Also, they sell little portable swamp coolers at WalMart, but they only cool a single room, and they cost more than $100. Or, the cheapest of all swamp coolers-- use a spray bottle to mist cold water on yourself-- it's not great, but it might get you through the night.