it doesn't take much to cause a problem with the rear defogger, you probably damaged part of the grid when you cleaned the window or something nicked it.
they are very cheap & easy to repair if you know how to do it.
to find where its damaged at & how to repair it, these 3 links should tell you everything you need,
http://www.glasslinks.com/tips/defrost1.htm http://www.fluke.com/application_not...AGID=1&SID=103 http://www.popularmechanics.com/how_...91.html?page=1
you should be able to find the repair kit at most parts houses,
Permatex 15067, Quick Grid Rear Window Defogger Repair Kit or
Loctite 15067, Rear Window Defogger Repair Kit
if you can't find it at a parts house, check here,
http://www.frostfighter.com/index.html