Time Machine and hard drive space problems...

t's a long story, but in a nutshell...I've had some problems with my time machine backups on my external hard drive and my MacBook Pro has been taking a long time time boot up. So, I decided to wipeout the backups on my external by deleting them (I know that's a bad idea) and then I started to transfer all the stuff from my MacBook Pro that I wanted to backup, and now I have ran out of room on the external (1TB) drive. However, the space that is being used doesn't seem to match what should be available. There is around 200gb (I think) that isn't accounted for.....is there some hidden stuff I might have missed?