Maybe you could try just working on one room to start with. Rather than look at it as one big job ahead of you. If you get one room tidy, then it's a start that may inspire you to move onto another room another day. Whatever you do though, don't move the mess from one room to another room. Find the right place for each thing, so it doesn't become a part of the next rooms clean up. Small steps, one at a time. Good luck with it.